What changes will push sch out of meta

[Shurrikhan]

AST already seems the theoretically strongest healer to me, so focusing primarily just on WHM:

Revamp the CNJ procs to make them more responsive and reliable than just mana reduction on sequential casts, thereby also making WHM more mana-efficient as an off-healer. That's basically all you need. SCH's advantage here is much like WAR's as an OT; just as WAR relies least on actually tanking for its damage output, the SCH relies least on sequential casts (actually healing) for its output over time. Level the responsiveness some. It's alright for WHM to still ramp up some compared to AST somewhat and especially to SCH, but it shouldn't be unreliably fishing for procs. And if a portion of WHM mana restoration should still be based on casts dealt, it should apply also to offensive casts, not just curative ones. It would be ideal if the replacing traits play somewhat into increased spell speed or oGCD spell-power, in order to improve WHM's sense of responsiveness.

Finally, you can improve their synergy with AST (especially Diurnal AST) by revising certain card effects to be more universally useful, rather than just situational, preferably without relying on absurdly strong effects such as post-buff Balance or its counterpart 'minute-long-Rampart'. If needed for either, you can also cause overheal ticks to "bloom", spreading to nearby wounded instead. I'd recommend possibly allowing for 'bonus' healing against heavily wounded allies, but WHM is already a strong enough progression healer. Unless DPS requirements are very high, it's during the farming period that it falls out of fashion.
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As for improving AST as a progression healer, the main direction is the same as ever: Fix the cards. Their tooltips might need to be expanded significantly, but they shouldn't so often go situationally to waste. Ideally, each should adjust group play somewhat. However, even should they end up about equally useful in most circumstances, albeit for different purposes, I'd still like to see more control exertable over the RNG components of drawing cards.

At most, you might add another spell or two involving card usage for added versatility.