I've leveled SCH to 80, toyed with WHM, haven't touched AST yet this expansion...here's what I've noticed:
First, as SCH:
I do like the idea of Seraph, and it is fun to use, but it's a bit wonky to have the double-charge Consolation that must be used within a 20s window. Further, it's kinda sad that Angel's Whisper is no better than Whispering Dawn (like what's the point of even naming it differently?), Fey Blessing would probably be nicer if it didn't have a cooldown, Fey Union feels weaker than ever.
The forced crit to galvanize is nice, as is deploying off myself.
Eos and Selene being identical is stupid.
Aetherflow is a problem...I mean, either I have nowhere near enough stacks...or I have stacks for days. There is no middle ground. It's also ridiculous that it can't be activated pre-combat when at least one other class (WHM) gets their full kit pretty much right away.
Overall, I feel slightly more capable on the healing side, massively nerfed on the DPS side, clunky overall, and it's boring to DPS. Yay?
Now, as WHM:
Healing feels as great as ever, possibly more so due to the WHM Lustrate (whatever the lv52 rose healing ability is), and I feel like I have more time to try and DPS.
DPS feels mostly the same as ever (I barely miss Aero2), and from the WHM in my static I've heard (and seen secondhand) the godly DPS that comes from the blood lily. WHM is in a good place.
Overall Thoughts:
It should be noted that the DPS difference is substantial...which the median WHM DPS being 17% higher than SCH (and rising as high as 20% higher as skill levels rise) while providing more substantial healing, having abilities that can stack with all other healers (including another WHM), better MP management tools, etc. I'm not sure if a 15% crit buff 12.5% of the time (net 1.875% crit if used on cooldown) to the party is necessarily worth bringing a SCH over a second WHM or an AST if a party is in a tight spot when WHM personal DPS might more than make up for that difference alone and an AST can give a flat 6% DPS buff to the party roughly 10% of the time while boosting individual members [such as the party's best individual DPS] throughout.
Sure, SCH does also have shields, but so does AST, so it's not like there's any special identity there.
A fix needs to happen for Aetherflow...several good options have been presented throughout these forums, such as returning energy drain (even if it just did MP restoration and no damage), having held stacks provide a buff to the fairy gauge, etc.
SCH AOE is way too expensive (basically a more expensive [albeit instacast] Holy without the stun [but a smidgen more potency] for 33% more MP), and without the MP management that WHM has...it's even more underwhelming. Something should probably be adjusted here, whether it's the MP cost or the potency (even if that means adding a cast timer to compensate).
If SCH is going to be primarily shielding or healing...the shields should probably mean more.
Seraph should be more meaningful (perhaps by buffing Angel's Whisper, buffing Consolation but taking it down to just one stack).
Fey Blessing shouldn't have a cooldown (even if we lost a bit of potency to make such happen), or it should be more meaningful to account for the cooldown (even if it cost more fairy gauge as a result).