I'll be blunt: I'm not sure the direction the healers are going in is the correct one. There's more identity stripping in an effort to balance the healers further, even though, if nothing happens, AST is still going to be the undisputed best healer for the same reason that SCH was the best healer in HW: The mechanics it has just allows it to excel. Now, we're going to have to pick one healer from column A and one healer from column B. Not to mention, this stripping of healer DPS probably had the opposite effect that SE wanted. I can only assume the reduction of healer DPS skills was to reduce the stress on healers to DPS, having lesser skilled healers feel more comfortable to DPS. However, lesser skilled healers aren't going to DPS regardless, and higher skilled healers feel even more pressured to DPS since a single lost cast of their main DPS skill just hurts so terribly.
So, that being said, what I wish they'd do for healers:
In general:
1) Return one DoT to each healer: Aero III for WHM, a new AoE DoT for AST, and Miasma and Bane for SCH. With an 18s DoT as well as it being AoE, this can feel like healer dps is slightly more active without it being overly complex like a true DPS role. This does mean a bit more for a healer to keep track of, but that's what healers generally want. At a certain point, most healers aren't even paying attention to party health unless they're really screwing the pooch on mechanics.
2) 1.5s cast times with the 2.5 GCD: This seems like a necessity at this point for WHM and SCH. The 1.5s cast time is really what allows AST to be so strong since it can DPS and use oGCDs without that much lost in term of Malefic casts. For WHM, they're expected to heal or clip their DoT before they can use important stuff like Presence of Mind or Assize, and SCH has to use Ruin II or their DoT as well. Ruin II isn't even a SCH spell at this point: it's a holdover from Arcanist. Like, it's kinda bananas that the job that's known for oGCD healing is basically punished for oGCD healing.
3) Piety gains an additional DPS benefit: Right now, Piety is a complete dump stat like Accuracy was before it was changed. Most healers would rather cut their piety down to 0 because it's really not that needed since most healing is done by Piety-less sources. It's mainly a cap on how many Raises you can perform before you're dry now. If Piety had some sort of dps benefit, then maybe my relic book wouldn't feel stronger than the Augmented tome book, which is 15 ilevels higher, btw. Personally, I'd like to see Direct Hit become DPS locked, but incorporate the Direct hit effect into Healer Piety and Tank Tenacity. This makes those stats more valuable since it carries something players like, and all the Tenacity/Piety gear has more of a use.
WHM:
Honestly, outside of what I mentioned in the general area, I don't think WHM really needs a whole lot. The only thing I would really change is how Afflatus Misery works. Instead of it only being usable when it has 3 charges and it being less than 3 Glare casts, have it be usable at any charge and how much the Blood Lily is open determines how many Misery charges you have. Oh, and on top of all that, it's directly equal to a Glare (or Glare II, if we get it) cast. This basically becomes a Triple Cast for WHM. On top of the 1.5s cast times, WHM will be extremely mobile, and that's good for a lot of kiting mechanics that exist in Savage content. Misery might have to be split into a single target version and a multi-target version that's proportional to Holy.
SCH:
Hooo boy. Honestly, if nothing changes about SCH come Endwalker, and SGE is at least competently built, I can't say many people will play SCH. At level 80, I shouldn't feel like I have an incomplete kit. Why can't SCH have a true Cure II equivalent? Or a shield less Succor? Why to I need to use a cooldown that has no other benefit than turning my shield heals into raw heals? It doesn't even make them heal for more or cost less MP. What is even the point other than counteracting Doom mechanics or having to cast a second Succor because you already used Indom? Oh, and let's not even bring up the fact if you, heaven forbid, died. SCH is probably going to need a massive overhaul.
1) Aetherflow, as it exists, is probably going to have to go. Aetherflow used to be a mechanic SCH got to access powerful oGCD healing tools with relatively short cooldowns at the cost of another resource and potential DPS. However, as the Expansions went on and the other healers also gained powerful oGCD tools, Aetherflow now feels like it's a punishment rather than a benefit. SE tried to get rid of Energy Drain at the beginning of the expansion which made Aetherflow virtually pointless and nearly non-functional. In 5.4, they nerfed it as punishment for SCH using it. It's painfully clear that SE does not want SCH to have Energy Drain. Honestly, I'd rather they scrap the whole thing before SCH becomes the next MNK.
2) Greater importance of the Fey Gauge: Right now, you can basically ignore this gauge and lose nearly nothing. It provides a rather weak single target regen and a healing AoE that is so weak and has such a long cooldown, I don't even know why it costs Fey Gauge. I'd like to see every fairy skill cost some fey gauge to use while these fairy skills have their cooldowns either removed or greatly reduced to compensate. It could be charged through Broil casts or Embrace casts if we ditch Aetherflow.
3) Two different fairies again: While I will say I think Selene, as she used to be, was not very good, I don't think making the fairies carbon copies of each other was the right move either. I'd rather see one be a regen fairy (Eos) and one be a shield fairy (Selene). While this will make Eos the stronger fairy 99% of the time, this does give Selene some niche again and not as glamour. Also, if we get rid of Aetherflow, I propose Dissipation (which is also a garbage skill, why does this still exist) becomes Double Summon, where you can bring out the fairy not currently summoned.
Edit: 4) Added effects for shields: So, right now, SCH shields are pretty bad if you don't get a Critlo. Not to mention Deployment is kinda clunky to use because Adloquium has a cast time. If SCH can get a true Physick II, Adloqium can become an instant cast for better use of Deployment. In addition, Emergency Tactics can get a new effect that kind of acts like an AoE Excogitation, but if the shield breaks before it falls off, the power Emergency Tactics/Excogitation will go up. It's not much of an added effect, but it is something that you can plan around using.
AST:
1) Flopping the sects of Collective Unconcious and Celestial Opposition: I think this change would bring the sects more in line with each other, also meaning AST might have to fall back on GCD healing more, which might lower it's pDPS contribution (which is a good thing for such a powerful healer)
2) Return Time Dilation: AST has a larger focus on single-target cards, making this a good skill for that purpose. However, I think if it was changed so that it only affected cards and not anything else, as well as AST being able to target itself in case its alone, it would be more fair.
Note: I don't think we can go back to the old card system like many people want for the simple fact of the matter is: It just took up too much of ASTs job skills. I mean, if we look at how ASTs job skills used to be, 4 out of 6 of the 30-50 skills were dedicated to card management. AST didn't even get it's AoE (Gravity) until 52. And if we look overall, Celestial Opposition, Time Dilation, and Sleeve Draw, as well as the Malefic upgrades left very little room for actual new AST skills. I mean, this is probably the most healing tools AST received at a single time.