Ultimately the combat design does not have room for more than 2 healers. The obsession with every job being able to do everything every other job can, and the frantic desire the devs have shown to strip all individuality from every role, but especially healers is nothing more than a curse. Sage in particular is very much a square peg in a round hole given it's a shield healer yet supposedly revolves around healing through damage. As the devs will seemingly neither accommodate innovation nor deviate from this path, the only course of action is to strip sage of either the kardia suite (such as it is) or the shield aspect - after all ast lost its sects.