The thing is, the whole double mana thing doesn't just end with healers
it affects everyone, say you get the debuff on a fellow ret, itl cripple him due to the tight rotation and low mana pool and the need to spam judgement when its off CD.
Current mechanics of the class isn't meant to sustain a rotation nearly as expensive as that one.
There's a difference between weakening a class, and then limiting them to autoattack