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[EDITED] - Altered information slightly as people have pointed out certain mechanics that I missed the 1st go around. Thanks everyone!
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I'll preface this by saying I'm a 73 Ironbreaker and so my experience is from my perspective having not played Blackguard higher than 25. These are my observations, but if they're wrong, please let me know as I'm always looking to educate myself more.
Additionally, I do not want Blackguard to be nerfed. I'm not intending to start a flame/rant war, I did my best to stay objective and just lay out some things as I see them. Much of these thoughts stem from a bit of jealousy in that Blackguards seem awesomely fun to play. I just want Blackguards to have some perspective on how their class is already compared to Ironbreaker, and not call for Blackguard buffs whenever Ironbreaker gets worked on. Which, by the way, the buffs outlined in OP's original post would be pretty insanely strong increases IMO.
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**Blackguard/Ironbreaker**
**Hate/Grudge**
Hate buildup on attack is an easier mechanic than Grudge buildup on defense. An Ironbreaker only builds up grudge when them or their Oathfriend get hit. A Blackguard builds up hate when either they attack or their Dark Protector gets hit; best of both worlds. Fighting an enemy that won't engage with you? You're out of luck as an Ironbreaker and won't build up Grudge. Ironbreaker ability damage scale hard with Grudge, so you're double gimped. Ironbreaker's can slot a tactic that makes it so they build up Grudge on attack, but you have to waste a tactic slot on that whereas Blackguard's get it for free.
Something to note as you read through the below abilities. Blackguard have numerous abilities that also scale with Hate, but several abilities that reach peak effectiveness at only 90H. Ironbreaker has more abilities that scale with Grudge, and none of them reach peak effectiveness before 100G. Most of the abilities become worse counterparts to the Blackguard version if you're under 25G or 50G.
**Morale 1**
All tanks get the same first two morales of Demolishing Strike and Champ Challenge, but Blackguard's get a 3rd that removes all hexes, curses, and ailments from the Blackguard and gains 50AP and 300HP for each effect removed. The Ironbreaker gets a 3rd morale that is essentially a second and worse Champ Challenge. It deals 900dmg which is different to Champ Challenge that deals no damage, but also just roots the enemy in place for 10s (same thing), but this CC can be broken unlike Champ Challenge. Whether a Blackguard ever uses Banish Weakness or not, you at least have an option that provides self-buffing benefits instead of what is basically just a duplicate spell.
**Morale 2**
Ironbreaker gets an ability to mitigate all damage for 5s in Skin of Iron. Without saying, that's a very powerful thing. Unfortunately, you would have to sacrifice Distracting Below (50% damage reduction for the group) to slot it, which would be a selfish play. However, in small-scale environments, Skin of Iron could save your hide for sure. The Blackguard alternative in this area is an AoE punt, but I'm not sure if anyone slots that. In theory, if you're fighting melee, an AoE punt also serves as a "damage immunity" by pushing said damage away from you. That might be a stretch of logic though.
**Base Abilities**
Monstrous Rending v. Rune-Etched Axe
Blackguard gets a spammable AoE ability in Monstrous Rending, Ironbreaker has no spammable AoE. Ironbreaker's equivalent is a relatively weak attack that ignores armor (25% @ 25G up to 100% at 100G) that is on a 10s cooldown. This attack's base damage is lower than Monstrous Rending and if you're under 25G when you use it, it ignores 0% armor. Again, if you're chasing enemies that aren't engaging, you're not building the Grudge you need for this skill to be at all effective. As far as I know (and this is where I could be wrong), the Blackguard is building up Hate on each enemy they're attacking. Monstrous Rending costs 30 Hate, but if you hit 6 enemies with it, it's free casting. If I'm wrong here, please let me know. But there are still clear advantages here with the Hate on attack buildup.
Murderous Wrath v. Heavy Blow
Blackguard gets a spammable single-target attack in Murderous Wrath that always ignores 25% armor regardless of Hate. The Ironbreaker alternative is Heavy Blow that deals a decent base damage with the potential for a large DoT over 3s. However, unless you're at 100G when you use the ability, the DoT damage is weak. Again, if under 25G there is no DoT component to the skill whatsoever.
Crippling Anger v. Binding Grudge
The Ironbreaker ability is actually slightly ahead here. Both skills apply an equivalent 10s DoT when used. However, Binding Grudge scales in damage with Grudge, whereas Crippling Anger does not increase in damage with Hate. Every 25G Binding Grudge increases in scale almost proportionally (25G=25% damage increase, 50G=50%, etc.). In game, if used at 100G, my Binding Grudge puts on a DoT that's slightly less than double the base damage.
Spiteful Slam v. Shield of Reprisal
Both classes can spec into a 3s knockdown while running a 2H build. When running SnB however, Blackguards get a knockdown that scales in duration with Hate to be the longest knockdown in the game. With even 60H, the KD is 4s long, with 90H it's 5s. The Ironbreaker's equivalent knockdown is still only 3s long, making it no different to the 2H knockdown except it requires a Block. One caveat here is that if the Blackguard isn't at least above 30H, then the knockdown is only 2s in duration. So while they have the potential to go to 4-5s long, perhaps this is still a balanced mechanic. But I don't see why they wouldn't make these skills identical as it's 2s with no Hate/Grudge, 5S with 90+ Hate/Grudge. Seems odd they wouldn't just mirror this CC. Additionally, Shield of Reprisal can proc on both Block and Parry, whereas I think Spiteful Slam is only on Block. So, potentially, the Ironbreaker's stun is available slightly more often than Blackguard's.
Exile v. Away with Ye
Blackguards get the longest super punt in the game. It does scale with Hate, so I'm not sure how much shorter it might be than the standard Ironbreaker punt if you're not rocking full Hate. However, at 90H it is loooong. But again, why not just mirror these abilities and scale the Ironbreaker's punt with Grudge? Give us the option to have the same CC utility too. While the damage component of a punt isn't priority, the Blackguard's base damage on Exile is double that of Away with Ye. I'm pretty sure as long as you're at 60H or higher that it's longer than Ironbreaker. Someone further pointed out that the Ironbreaker punt isn't any longer than the Chosen's punt with the tactic slotted due to the way it arcs.
Feeding on Weakness v. Vengeful Strike
Both abilities deal damage and increase the player's Toughness by 75. The Blackguard's requires only AP while the Ironbreaker's requires 10G, i.e. it's not something you can use right off the bat for a survivability boost. Feeding on Weakness also restores health to the Blackguard that scales with Hate whereas there is no health regeneration aspect to Vengeful Strike.
(nothing) v. Shield Sweep
Ironbreakers do have an ability that could help build Grudge in Shield Sweep. It costs 10G and can hit up to 5 enemies to regain 10G each, so a net 40 if you land all blows. But it costs 10G, so you can't use this as an opener to boost Grudge above the 25G threshold so many skills have. It's more of a way to regain Grudge at the top end (since we can't gain it by attacking) than it is to build Grudge quickly to start a fight. 1v1 this skill is pointless as you're using 10G to regain 10G on your target...
**Unique Abilities**
[BG] Mind Killer: 3x stackable Int/WP debuff. Ironbreaker has no stackable buff or debuff skill whatsoever. This skill coupled with 50% heal debuff tactic can hurt healers. The tactic components of this will be discussed later. However, a user pointed out that the Willpower debuff component is small (in T4 it's only around 75-100 fully stacked), so it's actually probably not worth the 3 GCDs it would take to stack this up.
[IB] Guarded Attack: Armor increasing buff, however, this skill becomes null in T4 as it doesn't stack with pots and is overwritten by stronger (and "permanent") buffs from other classes.
[BG] Crushing Anger: AP reducing damaging attack. Ironbreaker has no AP reducing skill.
[IB] Watch An' Learn: A 10s buff that gives 25AP back to our Oathfriend every time we attack an enemy. After the GCD expires it's a 9s window to restore AP back to our OF. Useful for guarding a Slayer who's AP hungry. With recent changes to Told Ya So! however, it's a bit of a redundant skill. But while BG has an AP booster, I don't think they have anything that directly boosts their DP alone. This skill also increases Weapon Skill but only for the Ironbreaker, not the Oathfriend.
[BG] Furious Howl: An AoE debuff that reduces all enemies within 30ft chance to Block and Parry by 10% while also dealing damage. Pretty self-explanatory how strong this is, Ironbreaker has no AoE debuff nor buff to counteract this.
[IB] Punishing Blow: An ability that damages the enemy and puts on a DoT on them that damages them as they move. A great ability to use on anyone, but especially those squishier targets that like to kite you. Blackguard gets no such DoT on movement. In my spec, currently, this ability deals 108 damage every 1/2 second while they move, leading to 216dps before mitigation. In the real world, it doesn't hit anywhere close to that, but it's still a good skill. The DoT is on movement though. If the Destro stops moving, the DoT stops.
**General Buff v. Debuff Mechanic**
The Blackguard is, overall, a debuffer while the Ironbreaker is a buffer. Buffs don't stack with pots and liniments and most other buffs override the Ironbreaker, so being a debuffer is infinitely more valuable in T4 as most of the Ironbreaker's buffs become pointless.
**Left Tree: Path of Malice/Vengeance**
Enraged Beating vs. Grudge-Born Fury
Both skills are important for DPS output. Enraged Beating is the #6 skill where as GBF is top-of-tree at #14. This makes GBF impossible to grab if you're also going for the self-heal (Blackguard can easily grab both) unless you have +2 gear like Warlord or off-Sov, but even then you have to make sacrifices. Additionally, Enraged Beating can be used whether in 2H or SnB whereas GBF is 2H only. Why this is, I have no idea.
Filled with Fury (tactic) v. Ancestor's Fury (skill)
Filled with Fury increases crit chance by 15% for 5s whenever you expend Hate to attack. Which, let's be honest, is all the time. Because this is a tactic, you aren't spending a GCD to maintain 100% uptime on the increased crit chance. Ancestor's Fury is an ability (so you're using a GCD) that costs 15G (now you're under the 100G threshold of maximum damage on your abilities) that only increases your chance to crit by 10% for 10s. But because you've used a GCD, that window is really just under 9s. By the time you potentially put up another buff, you might only have a 7.5s window. Also, you're trying to go for burst, but you've put yourself at 85G so your abilities aren't doing maximum damage anymore.
Malignant Strike v. Cave-In
Equal knockdown lengths at equal points in the tree, both require a 2H weapon. Ironbreaker's get a 5s DoT that scales with Grudge. However, if you're under 25G there is no DoT component whatsoever. Which, that's a lot of the time you're using a knockdown because you're initiating a fight. Also, side note, if you knockdown an enemy, they are no longer attacking you, which means you're no longer generating Grudge. A Blackguard can knockdown an enemy and continue to build Hate.
Hastened Doom v. Greataxe Mastery v. Stubborn as Stone (skill)
These aren't equivalent tactics but they are at equal spots on the tree. Ironbreaker gets a tactic that increases Parry chance by 5% and increased damage by 10% when running a 2H. It's not nothing, but Blackguard don't seem to get this, so, win. Hastened Doom needs to be broken into two parts. The first part is a huge Wounds debuff that, when coupled with FwF tactic and Monstrous Rending, becomes basically an AoE Wounds debuff.
The second part is the 50% Haste increase whenever you use Murderous Wrath or Pitiless Strike. Those two are key skills that you'd be using all the time anyway, so you are passively maintaining 100% uptime on a 50% haste increase. The Ironbreaker has Stubborn as Stone, which costs 5G to get a 50% Haste increase for 20s. After you use this GCD you're at a 19s window, if you're using other buffs and other things to setup further damage, your window is even smaller. The Blackguard is dealing direct damage in the fight while maintaining a crucial haste increase. Also, for anyone who thinks 50% haste isn't a big deal, take a closer look at how much damage you're dealing with just auto-attacks, it's large.
Crimson Death v. (nothing)
Another AoE damage ability that increases everyone's chance to be crit by 10%. That's humongous, especially in city fights. Increasing an enemies chance to be crit synergizes directly with your other abilities/tactics in this tree and directly benefits everyone in your group. Ironbreaker has no AoE debuff or buff whatsoever that combats this.
**Middle Tree: Path of Loathing/Stone**
None Shall Pass v. Oathstone
Same story as the Left Tree, None Shall Pass is the #6 skill while Oathstone is the #14 skill, making it impossible to grab multiple good utilities at once. None Shall Pass doesn't seem like it does a whole lot of damage, but it has a 5 Hate regeneration per block whereas Oathstone has no additional Grudge regeneration. Grudge is generated on being hit, sure, but this is just an extra gift to Blackguards. Like, "we understand while defending you won't be able to generate Hate for the next few seconds, so we'll put in a mechanic to make sure you can still do so." Oathstone damage heavily scales with Grudge, it's not until 50G is it somewhat stronger than None Shall Pass, at 100G it puts out 500 damage per attack which can actually be somewhat potent to the right target.
Anger Drives Me (tactic) vs. Oathbound (skill)
Anger Drives Me is a tactic that scales heavily with Hate, at 100 Hate it's a 30% Parry boost. Oathbound is a flat, slightly smaller, 25% Parry buff but doesn't scale with Grudge. This one is somewhat even, but I'd always give the edge towards passive bonuses rather than active skills that spend a GCD that could be used towards other abilities. Oathbound increases Initiative which is a small help to maintain 0% crit when there are Initiative debuffs out there.
Wave of Storm v. Earthshatter
So these two are equivalent skills but in different trees. I'd argue that maybe Earthshatter is actually in a better place since you're going for Grumble and Mutter along the way. I can see how Wave of Scorn could be inaccessible in some builds. Wave of Scorn has a flat damage that doesn't scale with Hate, Earthshatter scales hard with Grudge dealing 0 damage under 25G and max damage only if used right at 100G. But still, the edge here might be for Ironbreaker given the value of an AoE snare and it's positioning in the right tree and the damage potential Earthshatter has at max Grudge.
Shielded by Hate v. Shield Mastery
This one I'd definitely give the edge to Ironbreaker. Shield Mastery is both a constant 10% increase chance to Block and, while holding a shield, you only take 95% damage from all sources. 5% constant damage reduction will add up and I'd say this is a powerful tactic. Blackguard has a tactic that passively scales with Hate up to 10% Block at 100H, but I'm sure it more often than not fluctuates between 4-8% increase. So here, I'd say, the Ironbreaker has the better tactic.
Force of Fury v. (nothing)
Both an Armor increasing buff (which confirmed it does stack with pots, IB armor buff does not stack with pots) and a crit reducing skill for both the Blackguard and Dark Protector. Scales hard with Hate but peak effectiveness is reached at 90H (like the punt and knockdown). Ironbreaker is supposed to be the more defensive oriented tank but we have no skill that reduces crit chance. We do have a skill that raises Initiative which does reduce crit chance though (I think that max it does though is reduce 2-3%). At 90H this skill reads 45% less likely to be crit. Another person pointed out that it's not a 45% reduction flat out, but a 45% reduction of your already current chance to be crit (i.e. essentially a 5% chance to be crit taken to 2.5%), but I'd like to verify that with testing if possible.
**Right Tree: Path of Anguish/Brotherhood**
Unstoppable Fury v. (nothing)
There are two things right out of the gate in the right tree that are big boosts to the Blackguard. This tactic turns you into a healer killer. You automatically dispel detaunts when applied to you. Healers literally can't protect themselves from you anymore. This coupled with the 50% heal debuff is game over for healers. Blackguards, grab a Witch Elf buddy and go terrorize the back lines. Ironbreakers have nothing like this.
Shield of Rage v. Runic Shield
This one boggles my mind. Blackguard get their shield bubble for free while Ironbreakers have to spec into theirs... why this is, I have no clue. Not only that, Shield of Rage blocks damage from all sources while Runic Shield only blocks magic damage. Uh, what? Huge edge to the Blackguard here IMO, no question.
Choking Fury v. (nothing)
Because Ironbreaker has to spec into their Runic Shield in the #6 position, Blackguard's #6 is effectively an AP drain. Ironbreakers have no skill that increases enemy AP cost.
Soul Killer v. Punishing Knock
Both of these are the 50% heal debuff skills, but it's what skill they apply to that becomes imbalanced. Punishing Knock is applied to the Blackguard's equivalent of Brutal Smash, the STR and Willpower buff. Uh, okay. The Blackguard's, however, is put on Mind Killer, their Int/Willpower debuff. This synergizes perfectly. Why? Because you're already using the 3x stackable Mind Killer to debuff healing power, now you've reduced their overall healing effectiveness by 50%, and you're auto-dispelling detaunts. Goodnight healers, rest in peace.
Elite Training (skill) vs. Told Ya So! (tactic)
So this is where it makes me laugh when people are getting ruffled by the Ironbreaker AP battery tweak. Blackguards have already had an AP battery skill the entire time when Ironbreakers never did. Elite Training scales with Hate, again reaching peak effectiveness at 90H whereas an Ironbreaker never gets that luxury, and will restore a total of 60 AP to the entire group within 100ft. It's not a ton, but it's there. Also, in most larger fights, 4 attacks will fly at you in half a second, allowing this 60AP boost to be potentially almost instantaneous. Told Ya So! definitely has the ability to boost more AP over time, being a passive tactic that restores AP based on the Grudge used, but don't sit there and act like this tweak to Ironbreaker is unfair when Blackguards have had a similar utility the entire time when Ironbreaker never did. Again, this is also a tactic slot we have to burn. While passive tactics are still always stronger in scale than abilities, it forcefully burns a slot.
Shielding Anger v. Avalanche
Whether you take this tactic or not, it's a passive Disrupt bonus that can reach 30% at peak effectiveness. Ironbreaker doesn't have any Disrupt booster. Sorc and Magus hurt, a lot. What Ironbreakers do get is a tactic that increases our run speed by 30% whenever we do disrupt and gives us 90hp. This has synergy with Hold the Line (which increases your Dodge/Disrupt by 45%) so you can essentially HTL, proc the 30% speed bonus, and charge casters or catch kiting Shamans while healing yourself. I've never heard of any Ironbreaker burning a tactic slot on this, but I'm going to try it out and gauge it's effectiveness.
Unique Base Tactics
I'm not going to go through all the tactics, but these are just some standout ones that I think the classes would realistically use or that most people might have a "problem" with.
[BG] Thirst for Death: Whenever you crit you gain 10H, a great tactic to maintain Hate uptime, especially while you're spamming AoE and getting multiple crits. With this tactic you can theoretically maintain 100% uptime on Monstrous Rending spams.
[IB] Rising Anger: A tactic that allows us to gain Grudge now while attacking instead. So, it's clearly a better mechanic to build resource on attack, so much so that they gave us a tactic for it. But it's a big, big ask to burn one of your tactic slots on this.
[IB] Ancestral Inheritance: 660 Armor boost tactic. A great early on tactic that quickly loses it's value in T4 with the armor scaling from gear and other buffs. Most IB's end up not running this tactic after a while because of its relative ineffectiveness.
[IB] Sweet Revenge: 15% crit chance increaser above 50G. Sort of a replacement for Filled with Fury (15% crit increase whenever you spend Hate), but is still worse. Can be combined with Ancestor's Fury for a 25% crit chance increase so there's a benefit there, but this only comes into effect if you're above 50G. Below 50G, crit chance gone. Where as Filled with Fury is a 15% increase so long as you're expending Hate which, again, is probably all the time. But 15% crit is 15% crit, it's not nothing and this does increase the Ironbreaker's damage potential.
[IB] Seasoned Veteran: This is one where I'll give the advantage to the Ironbreaker for a defensive build. Whenever you block an attack you only take 85% damage for 5 seconds. With a 10% block chance increaser, and guaranteed blocks from Oathstone, you can proc this tactic somewhat often. As far as I know, Blackguards don't get any sort of large across-the-board damage reducer like this, so the advantage goes to Ironbreaker on the defensive front. What I don't know is if this stacks with Shield Mastery's damage reduction. i.e. Does Shield Mastery reduce all damage to 95%, and then Seasoned Veteran procs and you only take 85% of the remaining? Or does it only further reduce incoming damage by an additional 10% from Shield Mastery. Who knows.
[BG] Malekith's Bulwark: Not saying a Blackguard would run this, but putting it in here as a quasi-Seasoned Veteran alternative. BG's get a flat magical damage reducer (to 75%) that's not proc dependent. It reduces the healing effectiveness on you though by 15%, so, like I said, not sure a BG would ever use this, but maybe this helps against Bright Wizard pain. I know if Ironbreaker had a way to further reduce the pain from Sorc and Magus right now, we'd use it.
[IB] Seen it all Before: This is a good tactic if you can fit it into the 4 slots. If you're building defensively, surely two slots are already used by Shield Mastery and Seasoned Veteran. But this is one the Blackguard doesn't have. Snares last half the duration (which is average, we're all basically perma-snared in this game anyway), but also has a 15% crit bonus damage reduction which boosts survivability.
**General Thoughts**
From the above, it's pretty clear that Ironbreaker is supposed to be the defensive tank while Blackguard is the offensive tank. Blackguards debuff while Ironbreakers have a couple more self-buffs. However, as I explained earlier, the value from debuffing is fargreater than the value of a couple extra self-buffs. A debuffed target is that way for everyone attacking that target, an Ironbreaker increasing his own crit chance by 10% for 9s (after GCD) isn't really helping anyone. Also, most of our buffs are overwritten by pots, liniments, and other buffs. So, while we have a few tactics that gel better for defensive survivability, Ironbreakers don't really do enough for the group that benefits from gaining that added survivability.
The short of it is that Ironbreaker can be built a little tankier than the Blackguard, but there's no added utility to going tanky. Whereas the Blackguard can be spec'd significantly more offensively and have a ridiculous amount of utility along with that, with some of that utility and DPS potential still carrying over in an SnB setup.
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I hope that rundown made sense. I tried my best not to do any ranting and just be objective. Again, I don't want Blackguard nerfs. If anything I posted is inaccurate (changes to the game are made all the time) then please let me know. But I hope it paints a picture as to just how much better Blackguard is in almost every way than the Ironbreaker.
People might pull out the whole "this game is not about perfect mirrors" excuse, and I get that, but oof do Ironbreakers need some love. The good news? We're getting it, slowly but surely.
What more love do the Ironbreakers need? I don't know, that's not my job to balance this game. We have great people in charge of that. All I can do is lay out the things I see from my perspective and hope they help.