Let me start off by saying I’m not a healer main. I’ve played healers sorta casually since 3.X and the hardest content I’ve healed is extreme. That said, the healers in my static have said a LOT about what they think of the current state of healers and I’ve got some ideas.
The biggest problem with healing imo is that the game actively discourages using GCD’s to heal since the focus for every roll is doing as much damage as possible. Use a GCD to heal, you do less damage, you’re less able to clear and/or the encounter takes longer. Just feels bad. There are a few solutions to this.
The first is to go back to how healers worked before 5.0. Every healer had an actual rotation to keep track of instead of the current “dot and spam” that they have now. They weren’t super in depth or complicated like the other roles but were at least more interesting than they are now. For instance: scholar had three dots, one instant (bio) , one cast (miasma), and one instant with short range and short duration (miasma 2) made scholar feel unique. It also had bane which allowed them to spread their dots to multiple enemies which made dungeon pulls more fun. Better than spamming art of war at least. This option is probably the most likely as it wouldn’t mean having to change other elements of the game to fit like changing how much damage enemies’ auto attacks do or retuning raidwides.

The second option would require more work but I think would make healers feel more like they’re actually healers instead of green DPS (not saying that’s a bad thing for the record). That is, give each healer a damage refund for using GCD heals. White mage has this already in the form of the blood lily. Yes, the potency of it is off and there are some other oddities with WHM’s design so it doesn’t work perfectly but the basic idea is there: Use enough lilys (instant spells on the gcd) and they build up the blood lily which refunds the damage you would have dealt had you not had to heal. This means that white mages can heal, as their role’s name implies, without being penalized for it. I do think this could be expanded and the blood lily is just a good starting point. What could this look like on other jobs? Sage, my main healer: Using diagnosis, prognosis or their eukrasian versions grants an adder’s sting regardless of whether or not a shield breaks. Using toxicon substantially reduces the cooldown of phlegma. So much that you can gain multiple uses of phlegma throughout a fight. More healing gives you more damage. I haven’t touched Astro this expac so I don’t have any ideas for it but maybe using benefic/benefic 2 can give you a free card or something? My idea for scholar is (assuming it has all three of its old dot’s back) using any gcd heal gives you a buff to your next application of your dots. It could be a potency increase or longer duration or whatever. Perhaps even a chance to generate aetherflow stacks.