Give healer secondary identity more weight in their design.
WHM: Nuker. Let them weave oGCD heals with GCD damage and viceversa. High personal dps and healing.
AST: Buffer. Let them throw cards more often and let them extend, spread or ugrade buffs.
SCH

ebuffer. Let them weaken enemies with debuffs, weakening their attacks and exposing their weakpoints for increased damage taken.
WHM could use a more complex dps rotation they could weave with healing.
AST doesnt need more dmg spells rather having more options to work with their cards.
SCH doesnt need more dmg spells rather having more options to work with their debuffs.
There, solved healer identity without messing balance. The three can now contribute to group dps with either personal dps that doesnt stall healing, buffing teammates or weakening enemies.