I don't think it needs a complete rework, but it does need thinking about.
IMO the 2.0 design for SCH was fantastic. But there was 1) the perception that it was too weak, 2) shields did not stack so a SCH/SCH set up wasn't entirely great and 3) delay on faerie actions.
I think we just need an evolution of that design but with those 3 things addressed.
The perception that it was weak I think is what brought on what I felt were unnecessary additions to the job that inevitably made it OP and that was its boost to pure healing. So I think we should roll it back a bit again make its pure healing less efficient than its shield healing BUT don't completely nerf if its pure healing, they still need to be able to handle stuff like Living Dead and certain types of Doom.
In addressing the shield stack problem, I think one way this could be addressed is a to add a shield cap over Max HP. Eg if the cap is 40k HP, and the play's Max HP is 120k then the max HP + shields it can have is 160k, but say they drop to 100k, they could have a 60k shield because it doesn't exceed the 160k total. If I recall the reason shield stacking wasn't a thing is because it could mess with mechanics. But the real benefit of shield stacking would be when people's health has dropped and this is where it is kinda gimp.
The delay on faeries actions is an awkward one, and I hate they got rid of Selene's actions. It seems actions queue now, so I think that's fine, there isn't really much of a delay here just a queue, which you can account for, I've not found enough of an issue with how faerie actions work to complain about it (even if lament being able to properly micromanage pets, I know the problem that had and this seems like the compromise). Also modernise Selene, don't delete her.
As for the evolution part, healers now have more emphasis on oGCD's, I think we can shift more shielding onto the oGCD's to help shift some of the older design philosophy into how healers play.
I think having a tiered approach is a good idea, so people who want complexity can have it and the main reason SCH got OP is because its handicap got patched but it was that handicap that stopped it being OP. That handicap made SCH /feel/ weak, when played properly it wasn't weak. Like the perception DRK was always squishy but wasn't when played right.
As for WHM, I think it can be both simple and not boring. I reckon they could steal ideas from BLM's level 50 rotation. I suggested it in another thread but maybe something along the lines of:
Stone IV procs -> It becomes Quake (stronger version of Stone)
Aero II Procs -> It becomes Tornado (delivers total Aero II damage at once)
Dia -> This becomes a debuff (WHM utility), perhaps a defense debuff
Glare -> I thought it could work as a lily dump and build up for Afflatus Misery
It's not complicated but it adds variety straight away. The healing side is already pretty fluid, but I think upgrading the DPS side like that could help break up some of the monotony whilst remaining simple.
And I think then both its healing and DPS would lend to WHM being the "powerful" healer and with SCH retaining a "tactical" healer and maybe AST as a "technical" healer.