Your post is really amazing thank you for that!
I personally don't play any healer but my brother plays all 3.

First of all the AST card changes are just a joke, I don't understand the SE trend with just DPS buffs on everything(devotion for SMN or pruning utilities like Palisade). From a job which is unique to a job which lacks just any kind of uniqueness from the other healers(though for the "meta" AST is going to be just insane).
WHM players were mad about some things, with for example the Lily system(which is now just waiting(not really engaging)) and not being able to be part of the "meta", now get nothing for the "meta".

Now we go to SCH.
These changes now are totally insane in a personal and watcher perspective. They do not help WHM problems because Chainstrategam is still being there.
Oh and WHM is also losing Aero 3 just like SCH is losing Miasma. SE could have kept the castable DoT to provide more skill and management for the player.
Another point is the Fairy. You cannot really manage her, Selene and Eos are just the same and even though they have another heal now, there would be more time to manage the DoTs but instead they cut them.
Energy Drain and Shadowflare is also huge. Not being able to do anything with the Aetherflow Stacks and just waiting is just not engaging.
I use the word engaging because SE is always talking about engaging gameplay but the Healers lack engaging gameplay. Even the Lily system is not engaging because you just wait. The Aetherflow system is not engaging anymore because you just wait for the group to get damage and use for example Lustrate. AST cards are not engaging because you just use them on a Melee DPS or Ranged DPS.
The whole engaging and unique playstyle is gone from the Healers. Even if they got new heals, the gameplay will not be engaging as before.

The presentation from the Live Letter about the Healers was really disrespectful towards healers. They don't bring a new Healer, they almost speed-talk the Healer changes in the Live Letter and do not show any footage. They even almost cut the talk about the Healer-DPS but later on said just 1 sentence about it which said like nothing.

Also it is pretty easy to balance the "meta" for all healer be viable. Because the main problem of the "meta" is utility buff like Chainstrategam or Cards. Therefore they can just give WHM a utility as well.
But personally I really don't understand why they only try to balance on the Savage Raid "meta" style. Where is the unique Modern-MMORPG Style of FFXIV where they focus on Story, job identity, progress of the character, nuanced gameplay? I am really sad that the go the action/arcade way instead of the nuanced unique story way. Why does SE want to balance something where they forbid these programs which provide DMG metres or w/e?
I really do not understand them, not even 1% of the community plays "meta". They seem to not understand the community and healer playerbase at all I guess.