best take with zero solutions in sight because that would mean reworking 4 jobs, or reworking the platform they're in. with the best case scenario being the healers are harder to play which will anger the casual audiencePerhaps it would be useful to approach from the opposite direction: take a kit widely considered "good", and play evil job designer with it. Make one change that would absolutely slaughter the kit's fun, and you've probably discovered some key magic that makes the sausage machine work.
What if, for example, we removed the distinction between black and white mana on RDM entirely? Fold them both into Red Mana. Every spell effectively a Jolt. Suddenly you've killed all interactivity in the casting and burst phase. Overrode a proc? Who cares. Used your spells in the wrong order? Ehhh. Disrupted the flow between your black and white spells? Doesn't matter. Choice between Verholy and Verflare? Don't care.
I think one of the most core things that makes a job fun is meaningful choice. There's a lot of flexibility there; the choice can be largely illusory or superficial, as you might know the black/white mana flow is VERY forgiving. It could stand to gain some skill ceiling from there; lord knows I miss the minor optional optimization game that was potency-gain Reprise, murdered in Endwalker.
Most of the healer kits are aggressively unfun because they're so childproof that they're essentially Red Mana jobs. Did you use the "wrong" heal here? Trick question, there isn't one. You aren't punished for basically anything outside death or healbombing so hardcore you deplete your MP. Oh no, I used a lily on the full HP ninja by accident! Oh wait who cares, I got the refund anyway. Oh no, I used Indomitability instead of Sacred Soil! Oh who gives a crap, they do practically the same thing, have exactly the same reward for using them, and barring tight mitigation checks or highly preplanned minimalism nobody will care, not even you. All of the kit "interactivity" is of the passive sort that has little to no influence on the decision tree. Kardia's up on the tank? Such interaction, wouldn't it be nice if it made me think twice about Dosis Dosis Dosis Dosis Dosis Dosis Dosis. Plenary Indulgence? It's Yet Another Healing Steroid. It doesn't change how you interface with your casting flow or introduce any decision-making. There is not a single moment in time where I wonder what my next ability will be, because if everyone's HP is fine it's just Boring Damage Nuke and if it's not, I could probably throw my healing buttons in a hat, fish one out at random, and be rewarded or punished more or less equally.