I mean on paper the niches are easy:

* AST and WHM are focused more on regen and re-healing.
* Meanwhile SCH and SGE are focused on pre-emptive mitigation.
* Also AST and SCH are focused more on utility effects and "tricks".
* Meanwhile SGE and WHM are focused more on raw output and "power".

The funny thing is, this works except for two spanners the devs "usual" pitfalls throw into this, and sadly for Ultimate purposes they entirely break the balance setup's back:

* The extra power in healing exists, but with how meaningless maximum healing output is - since you virtually never want to get caught in a situation where that is needed, you want to heal it all with your CDs - it just has absolutely no bearing on effective use.
* For balancing reasons they opted to make the damage output the same, which doesn't work as due to their niche, WHM and SGE would need to deal more even with the extra RDPS from cards/debuff included (and Picto being so OP also indirectly adds more AST/SCH damage and this would automatically be fixed if they finally curb PCT damage and downtime enjoyment).

But yeah, on paper it's easy. AST and SCH bring all kinds of cool utilities, but WHM and SGE heal and nuke for more. Meanwhile AST and WHM can re-heal, SCH and SGE can "pre-heal". Easy.