1 Why cast heal WP/DoK are mandatory, in both small and large scale
Let’s start with small scale. WP/DoK simply have the highest healing output compared to RP/AM/Shammy/ZL. Their single target healing I guess is comparable to the Shaman/AM, but next to the strong single target healing, they have by far the best AoE healing. Now it is easy to point at backline WP/DoK and say how OP they are, but in my eyes it is the combo of RP + WP and ZL + DoK that is really strong. The ZL/RP buffs the healing output of DoK/WP by 25%, gives a stagger to catch people and can somewhat reliably silence the enemy healer. Double WP is sh it and I personally also believe double DoK is quite a bit worse than ZL/DoK.
Next to the strong healing WP/DoK has a standard high armour so it can into the front lines. This extra armour makes it easier to survive being focused BUT it is not the case that they are unbillable. And the way the WP/RP and DoK/ZL functions it is quite often better for the RP/ZL to be focused than the WP/DoK. That is because when the WP/DoK being focused the healing output of your highest healing output healer goes down. While when the ZL/RP is focused they can maintain the 25% more healing buff on themselves, they have an instant heal cast, so they are not effected by setbacks at all. I want you to understand that it is not just WP/DoK are so OP, it is the WP+RP and DoK+ZL that is superior in terms of survivability and healing to any other healer setup.
For large scale it is quite a bit different. Why WP/DoK is so strong for large scale is very simple: They can maintain high AoE healing while staying very mobile. An AM can probably come quite close in terms of AoE healing because of basically infinite AP and just spamming group heal, but they become very stationary. (Shaman lacking Wild Healing will run out of AP) For large scale it is not just the high armour that makes WP/DoK strong, in fact a lot of large scale damage is magic damage, I believe it mostly is because of the mobility + strong AoE healing.
Before going into how the mandatory status could be broken I want to talk a bit more about the playstyle of the WP/DoK. So let’s talk about the current optimal way of healing, even though I’d rather not give it away but since it’s going to be changed anyway w/e. For maximum healing output in both large and especially small scale you have to be in melee range of something you can attack. It can be a pet, turret or player it doesn’t matter. But the most effective way to get your RF/SE back is through attacking enemies with Sigmar’s Radiance and Transfer Essence. On my WP I hardly ever cast Supplication to regain RF, I generally just spam Sigmar’s Radiance to maintain RF WHILE also healing. This means that the current optimal way to play is generally to play as a melee. A big but though is when the enemy runs a BG with the outgoing healdebuff. This basically forces you to stay away from the enemy melee train and just by the threat of the BG, it reduces your healing output quite a bit. (Same for IB and DoK ofc)
For large scale the same is true, attacking with Sigmar’s Radiance and Transfer Essence is the most optimal way to get your RF/SE back. Also because you keep your mobility, while if you have to cast Supplication or Blood Offering you have to stand still for a while. Smite and Essence Lash can be used when you are not in melee range of 1 target but can hit multiple targets with your AoE, once again keeping your mobility.
Lastly please stop the bullshit that WP/DoK healing is super easy. The healing part of WP/DoK is actually very skilful. Maybe the skill floor isn’t too high, but playing an optimal healing WP/DoK requires a lot of skill and there aren’t many that can reach it. The experimental changes increased the skill of AM/Shammy by quite a bit, but without those experimental changes DoK/WP is simply the most skilful healer in terms of healing output. What makes a lot of people say that WP/DoK is easy is their free survivability because of high armour. But as I have illustrated in the beginning it doesn’t work that simple in the highest level of play. Of course it is very nice to have that extra armour, but at the same time you don’t have the kiting tools like the other healers so you would be quite screwed without it anyway.
Not on topic but the melee healing in current state is a lot easier than backline healing 
2 How that mandatory status is to be broken.
This is quite hard because the DoK/WP has different strengths in both small and large scale. For large scale its main strength is its mobility while doing high AoE healing. For small scale it mostly is its superior healing output. The approach Azarael seems to want to take is completely split backline healer and melee healer. I personally am more in favour in hybrids between these two and leaning more towards either side depending on the situation. As I’ve said, playing in melee range is already favourable compared to staying at range all the time. By strengthening this effect you could bring former backline WPs/DoKs more into melee. But when you talk about the mandatory status to be broken, it should be a combination of changes to DoK/WP and also the other healers. Like whenever you have a standard healer you want to combine it with a RP/ZL. But there is not a single point in running a ZL/RP in combination with a melee heal DoK/WP. AM/Shaman with the experimental changes have really strong single target healing output, but lack a bit of AoE healing while maintaining high single target HPS. Same could be said for RP/ZL.
There are so many ways you could break the mandatory status but I personally believe it involves improving AoE healing of the other 4 healers. This is especially the case for large scale. Next to this I would suggest making it stronger to also be in melee while still playing mostly caster WP/DoK with Book/Chalice. Whatever strength you give should be taken away by the casts itself. I’m going to give a simple example but there are probably a lot more fun and interesting (and possibly skilful) ways. The example would be to increase the base heal of Sigmar’s Radiance/Transfer Essence and nerfing the AoE heal from Touch of the Divine/Khaine’s Embrace.
What I am personally against is to have different heal stances. I can agree with a pure dps stance because it deals with the issue of having too much damage while still being able to heal a lot. By reducing the healing of pure dps WPs/DoKs you can turn them into full dps with the damage of pure dps classes. But for healing I think the most skillfull way to play is to play something between full ranged and full melee, that is as replacement for the backline healer. In that sense I would suggest not to mess up the armour values of the WP/DoK because if you do and force them to play as full ranged you also have to give them ways to kite and in my opinion it just doesn’t fit to the class.
I’m not giving very concrete changes for now because I should really think carefully about what changes would do well. Also I have only written about “backline” DoK/WP, but it will be quite a challenge to make both backline DoK/WP and meleeheal DoK/WP work good together (as changes to one not make the other OP).
