Optimal play for every single one of these proposals would involve ignoring a significant portion of the toolkit. Every single class you proposed would change useful abilities to "take this off my hotbar and pretend it doesn't exist" trash.

WHM
WHM's weaving and mobility spells are sparse enough. Anything that decreases that exacerbates the problem. Making Afflatus spells have a cast time eliminates one of their biggest benefits.
Cure I/II serve no function with Afflatus Solace being higher potency and generating a Lily 100% of the time. Throwing these in the trash as soon as possible. Toss Regen in there while we're at it, because it costs four times as much damage to use Regen as it does to use Solace.
Medica/Afflatus Rapture generating a Lily makes Medica II 100% obsolete. Each cast costs 75 Potency compared to 300 potency for Medica II. They have higher burst healing, too.
Increasing Cure III's potency by 50 for no reason is making a change for its own sake. Waste of design space and developer resources.
Splitting Misery into single target and aoe versions achieves nothing apart from button bloat.
Your changes to Divine Benison turn it from a bit of free healing to a near-worthless waste of a button. Making it instant would make it helpful for weaving or movement, but costing a full GCD (300 potency) makes it far more costly that clipping or dropping casts to move (unless the movement is longer than 2.5 secs).

Additional note: the current Lily system (ie. placing them on a CD) gives skilled healers a strong tool if they can manage the resource properly. Lilies provide movement, weaving, and incredibly cheap healing at the cost of a finite resource. Other healing spells hold their value for when Lilies run out. The more efficiently a WHM heals, the less they need to pay full cost to heal. Your implementation would cut out the mobility and weaving rewards that Lilies provide, introduce unlimited "participation award" damage refunds, and render several defining WHM abilities obsolete.

Optimal play: Dia, then Glare Spam. Use Afflatus Solace for single target healing. Use Afflatus Rapture for aoe healing. Hold Afflatus Misery and Bloom for movement and weaving or to prevent overcapping. Lucid Dreaming, Thin Air, Assize, Asylum, Tetra, Benediction all used as current.

I didn't think WHM gameplay could be made any more mind-shatteringly boring, but you managed it. Well done.


SCH
Before anything else, doubling shield potency is going to seriously alter how mitigation and surviving lethal damage mechanics will need to be designed. Either SCH is going to be able to solo mitigate everything, or AST will be incapable of providing sufficient shields.

Gaining aetherflow from shields breaking isn't a terrible idea, though the system as a whole is a mess. Optimal play will involve using Adlo or Succor once every 90 secs to be able to use Biolysis every time dots need refreshing. That frees up one Broil II per 30 secs. Placing every aetherflow ability on the GCD means that every one of them will be avoided as much as possible. Energy Drain doesn't restore the MP it takes to create a single aetherflow stack. Lustrate heals less than Adlo (400 vs 300+750 shield). Deployment Tactics takes two GCDs to spread a 562.5 potency shield compared to Succor's 450 potency in one GCD. Overcapping on aetherflow doesn't matter at all because spending it is a mistake in almost all cases.

Fey Blessing uses the same GCD as Succor for a weaker heal. Only use case will be for intense healing checks where the SCH needs Succor > Fey Blessing > Succor because of the delay on shields becoming active after being applied.

Your changes to faerie gauge will lead to it only ever being used for two things: Whispering Dawn and Aetherpact. Using it for Aetherpact is horribly suboptimal, but will save a lot of hassle.
Summon Seraph will take 150 secs worth of aetherflow generation to use. Not worth anywhere near five Whispering Dawns.
Fey Illumination's damage mitigation is worth far less than Whispering Dawn.
Consolation is in the same boat as Fey Illumination. Simply not worth passing up a 700 potency hot.

Embrace is where we see just how poorly thought out this system is. If we assume it'll be weaved 20 times per minute then the SCH needs to devote 60 APM to target their ally, hit Embrace, then retarget the boss. AST needs to do this three times during Sleeve Draw and people hate it. I guarantee that almost every SCH will stop using their faerie or change to a new class if this is implemented. This is the worst instance of UX design I have seen in my life. Aetherpact gains value solely because Embrace is so terrible.

Optimal Play: Miasma > Bio > Aetherpact > Broil + Embrace spam > Biolysis at 30 secs. Repeat, replacing one Broil with an Adlo or Succor every 90 secs. Set up a keyboard macro for Broil > Target of Target > Embrace > Target of Target. Whispering Dawn for everything else. Lustrate self during downtime to build Faerie Gauge if excess aetherflow has been generated.

Riveting. I really love how you made almost every tool compete for either GCDs or faerie gauge so we can find the optimal action in 30 secs of reading and thoroughly ignore everything else.


AST
Draw is GCD. Using that card must provide at least as much rdps as is lost from not casting Malefic. Play is also GCD. Cards need to be worth two Malefics just to break even. Cards must never be played on a tank or healer because they won't give any damage. RNG damage mitigation and healing boosts are worthless. A 6% damage bonus for 15 secs is worth 18k damage if applied to someone dealing 20k dps. In other words, less damage than a malefic when put on a high performing dps. Even in the spikiest of cases it'll never be worth giving up two malefics. Minor Arcana is equally useless. So AST doesn't want to play cards at all. Off to a great start.

Earthly Star loses damage for no reason and becomes aoe Benediction. Current Earthly Star is great because optimal use involves figuring out how to get the maximum healing from it when using it as close to on CD a possible. Now it's just a delayed heal with an insane buff. For reference, fully healing a healer requires around 2200 Potency of healing. Tanks are closer to 3600 potency. At least WHM won't be the only healer to cheese Living Dead now.

Changes to Benefic and Benefic II are fine, I guess. Benefic I will be ignored entirely, but that's nothing new.
Turning Essential Dignity into a GCD and giving it less potency than Benefic II makes it entirely obsolete.
Horoscope's change is interesting, but there's no need to make it GCD. 800 Potency is enormous. Helios and Aspected Helios are obsolete and can be removed.
Sleeve Draw helps reduce Draw's GCD impact. It may be worth using cards on some classes during their burst windows, but if they're not dramatically better geared or at the top of their field it's still a dps loss compared to Malefic spam. Would need to review logs extensively to determine when it's worth using.

Cards might pay back their Malefic cost if they are only used to prepare the next Divination, but it would require significantly above average players in the party.

Optimal Play: Combust > Malefic spam. Celestial Intersection for single target healing. Benefic II after that. Earthly Star + Celestial Opposition + Collective Unconscious for aoe healing. Horoscope if that's not enough. Play cards during down time unless you've reviewed logs and found times that Sleeve Draw aligns with other players' burst windows but not party buffs. Ignore cards in 4-man content unless they can be used between pulls.


Conclusion
With respect, have you ever actually played a healer? Your changes do nothing to fix any of the problems that healer jobs currently suffer from, fly in the face of encounter design, and introduce optimal gameplay that involves ignoring up to half of a job's abilities. I'm not one to praise how the devs handled healers in ShB, but that looks like the product of a Mensa think tank compared to your suggestions. I sincerely hope these changes never get implemented.

In case this is anything other than a high-effort troll attempt (you got me if it is), the problems with healers isn't their GCD healing and they don't need more of it. GCD healing is somewhat bland and isn't interconnected at all, but that's largely made up for with the vast array of oGCD healing that's available. The root of the problem is the lack of meaningful downtime activities. Moving oGCDs to the GCD can partially help overcome that if all of the GCDs are unique and fill their own niche, but your implementation has far too many trap abilities for it to work. The fundamental flaw in your suggestions is ignoring the opportunity cost the the GCD presents. I'd like to see meaningful GCD healing. I'd like to see Play put on the GCD. But if the lost Glare/Broil/Malefic isn't considered when making that change then it cannot be implemented well.