They can make raids hard without nerfing healers like someone said make these aoes place healing debuffs or cause dots, with how healing is now those are he main things I see healers fall at which is dot dmg, and the occasional healing debuff...

You can also have some raids have a boss that removes shields from the raid or disables certain actions by tanks like a CD maybe but the point is there are other way to go about this then nerfing healers