I think that's make DPSing interesting in FFXIV are burst phase. Once the baseline rotation is learned the DRG baseline is not much less boring than healers today. Taking this in account, i would like to propose some CD abilities and ressources managment to some healer. So that i would like to see

WHM : as he already got some cool looking abilities (misery) and a burst button (presence of mind), there is no need to add. So to give some ressources management :
- Add a ressource bar : for each cast of Glare/holy and each dommage tick from Dia you get some. With a cost of 50 you get a instant cast AOE GCD dommageing spell (water base for design) with falldown dommage.
- Just reinforcing Presence of Mind with a free misery cast.
The blood lily system is working fine, so i don't want to touch it. Misery looks good and feel good to use, so giving an additionnal cast on burst seems fair to me. I didn't think adding an additionnal dot to track to be nice, and an offensive no cast time GCD is lacking on WHM

SAG : He already gome some CD gcd, i think a cool addition to the kit would be :
- Laser focus : a simily flammethrower : you cannot move and for the next 5s you hit the targeted enemy each seconde. Kardia also apply as reduced rate for each tick. 60s cd
I think the sage should stay very straightforward. I think flamethrower is a unique ability in the way it's work and should be extended. 5s duration may be a bit short to be involved, having the ability to proc Kardia seems mendatory to me, but not at full at it would lead to a big kardia heal for the duration.

SCH :
- Maybe add a 2nd dot
- Use a aetherflow grant aetherfairy, aetherfairy change Ruin 2 for "Fairy Ruin" which does more dommage than Broil 4. Max 3 Aetherfairy
- Chain Stratagem is vastly empowered : give 3 charge of Fairy stratagem -> allow the cast of Fairy Ruin (same as AetherFairy but cumulable) and 1 charge of fairy blast -> Allow to use a powerfull dommaging GCD with cast time.
The schoolar is lacking of ability to use on burst opportinities, so I adding one. While ruin 2 is a nice tool in Schoolar kit, it's the only move tool he had and feel base to use, so having en empowered one from time to time seems nice to me.
The 3 free fairy ruin on chain stratagem is to me the best way to prevent some wild use of aetherflow (which should be used for heal) for extra DPS, as having 7 GCD to use on burst if you prepare it well should cover most of burst timer.
In addition to theses changes, i would also change the aetherflow ability itself :
- Deletion of energy drain
- Aetherflow got 2 charge, 40s cd. Each cast grant 2 aetherflow and 1400MP, 3 charges Max.
--> I trully dislike energy drain as it is, but it's necessary as no using aetherflow also impact aetherpact capacity.
--> I think aetherflow is actually to rigid to fully work with. You need to spend all flows in 60s, maybe rushing when you got 10s cd left, and nether delay it's use. My proposition left the nomber a flows unchanged, and allow to delay the use for maximum 40s which is more than enough to burn unused flows before getting others.

And I don't have any idea on AST, as I think card could be some kind of basic offensive ogcd and some other stuff, but it would be very unpopular.