SE should embrace healers secondary identities: SCH as a debuffer, WHM as a nuker and AST as a buffer.

Give each a system as complex as the AST cards use to be to fill the healing downtime.

Have SCH use AF stacks to find enemy weaknesses and reveal them with Chain Stratagem to create burst windows.
Have WHM water the lillies by weaving together healing and damaging spells.
And AST focus on aligning buffs, extending and changing them to fit the needs of the party.