At first glance it seems like a good idea but I see an issue with Shatter Limbs, the one ability that gets Slayers warband spots, the ability that requires them to be in the thick of it - in the backlines - in RvR combat, being at the top of the tree that makes Slayers the least survivable.
Slayers will have the option of:
a) Running SL and Power Through, going into the backlines and hoping they can drop SL and do some damage and drop a second SL before exploding or
b) Running SL just for the sake of the debuff and not going with the 2h Giantslayer playstyle and being durable enough to actually make debuffing back lines with SL work.
c) Running the standard ID AoE build without SL hoping they get a WB spot.
Either way it feels like the Slayer viability would suffer.
I only have experience running ID/SL in a WB setting (on live) and don't know if/how durable Slayers with Power Through are in RvR. But it seems to me that if b) occurs then SL is clearly too strong (a career is viable as being only a SL bot with little else to offer).
My suggestion would be keeping the spec tree's you've laid out but swapping ID and Shatter Limb. Remove the AoE component on ID (and the dualwield requirement) and buff the damage SL does to approx the combined aoe damage value of ID.
(Stealing the neatly edited picture, kudos)
The reasoning would be:
- Skavenslayer becomes more difficult to spec for but Slayers speccing for it can retain their role of AoE support dps. SL would become not just a debuff with minimal damage but a strong AoE damage spike. Adjusting the cooldown appropriately would be justified (and perhaps tone down the order dominance on CD increasers).
- ID is a strong single target damage tool, it's also very unique and I'd hate to see Slayers lose that. If you combine constant ID (changed to single target) with the strong spike tools Giantslayer already has you turn that into the dominant single-target spec tree.
You solve both SL being too easy to obtain while mainting the role of Slayers in a WB and Giantslayer being overshadowed by the other two specs. Skavenslayer would become strong AoE damage while Trollslayer maintains its position as a utility/durability tree. Also you kinda give Slayers the choice between a Power Through 2h Giantslayer spec and a Dualwield "Giantslayer for ID, rest in Trollslayer, spam Spine Crusher" spec.
The problems I can see are
1. SL becoming too strong (although it feels like damage is already in abundance in WBvsWB) or too weak - perhaps the damage on SL couldn't be buffed enough due to burst constraints for the spec to be doing enough AoE damage without ID and would run into the same issue as TenTon's suggestion.
2. Giantslayer becoming overpowered with the constant damage of ID combined with the spike of Deathblow.
3. You're not exactly restricting Slayers to 2h when speccing to Giantslayer. I'm not sure that's an issue but it feels silly if the main spec would be Dualwield Giantslayer spec that uses no GS abilities except ID.