The problem with healers is the same with tanks.
Sure in theory the idea of a healer that isn't as good at healing as the other healers but does more damage sounds good on paper but in reality it becomes a balancing nightmare just like a tank that does more damage but is easier to die.
Part of the reason ED works on SCH is because you only use it when theres no need to use your aetherstacks and know when you next need them you can regain them or use recitation, you can't really have a support thats traded off to be bad at their support role but good at damage because then why not just replace it with a DPS at that point. If you need healing then you'd take the better healer. Its why the whole WHM design idea that people talk about procing sacred sight off of a cure or just having heals in general combined with DPS is very iffy for me, I prefer having the healing and DPS completely seperated because then you can balance them individually and you won't have the endgame version of freecure procers being sacred sight procers.