The healers dynamic isn't much different from the tanks one.

There's a lot of occasions where you don't need 2 tanks and one ends up being a weak dps. Which is essentially no different from the ops 2 healer issue.

And it suffers the same problems as well. I.e

What happens if duty finder pairs up 2 dps healers as the op called them into the healer slots of a group.

That group is going to be lacking a lot of healing power. Especially if those dps healers only have 15-20% of a full healers restorative output

Same with tanks and why they don't vary much. One of the issues with pld is the dps loss from having 2 in the same group. But 2 warriors or 2 darks ldon't share the problem.