I keep getting into healer threads and essentially repeating the same thing.

Build on each healer secondary identity.

Their healing is homogenized? Have their contribution to dps be distinct.

AST has its own way to contribute to rDps: Buffs. Give them more tools to manipulate said buffs. Let them cast cards more often, and have divination be more impactful. Card management is what makes the class unique. Double down on that.

SCH is the debuffer. Make Chain Stratagem an equivalent of divination, in the sense that it becomes an ability that requires tactical build up. Give them debuff management, skills to reveal weaknesses, exploit gaps in enemy defenses. Have them apply strong enfeebling debuffs while the fairy sustains the party during those times.

WHM is fine with having no utility as long as it contributes with enormous personal dps. Make lilly abilities into oGCDs, let them weave damage and healing together. Have fluid aura deal moderate damage and increase the speed of lilly growth when woven with other spells.