Giving us a button that we press more than once per minute (or once per 2min if you're SCH/AST) would be a nice start. I think their insistence on the stance of 'healers shouldn't feel like they're forced to do damage' is hamstringing them in so many ways that they themselves might not even realize. Just accepting the idea that, if we're going to have 90% of our gameplay time in certain content be 'do a damage action', and adding more damage actions to fill that time with more variety, well, the creativity will naturally start flowing more, and they'll likely find all sorts of 'new' ways to expand the Healers and make them feel distinct from one another again
Consider how much more active SGE would feel if Psyche was a 30s, 300p attack instead of a 60s, 600p attack. Same damage, but you use it twice as often. Or what about if we go a bit crazy with it, and have it as 150p and 15s CD, with 2 charges to help avoid overcap? And hear me out, what if we then also had it then synergize with the rest of the kit, eg by making it trigger an instance of Kardia healing? And this would then synergize with Soteria, by allowing you to get through its stacks faster and thereby push out more healing when it's needed, and then what if...
So we can see, from a single idea, an entire design can bloom, by just following the 'and then' chain and seeing what comes of it.
Take me for example. I'm just one forum user, but I had a crack at reworking the Healers to spice up the gameplay anyway, because, well, I thought it'd be fun to try. Take the SGE idea, I began with nothing more than the idea of 'I think it'd be cool if Kardia was an actual system to optimize around', yet after a lot of 'oh and this would be cool' feature additions/revisions, the final form of the design has ended up being a fast-paced, RPR-Enshroud-having hyper-offensive (read: appeals to a DPS player mindset) Healer job that simultaneously has a very high skill ceiling, but also being incredibly low-floor/forgiving due to having no MP cost on any of its basic GCDs. Would it be well received? Maybe, I dunno. I imagine there'd be some who'd dislike it, and some who'd like it, just as is the case for every job in the game. But I'd rather gamble on 'a non-zero number of players might dislike it' than the current 'play it safe by changing almost nothing, every time' we have been getting for some years now.
Still waters grow stagnant. The Healer role's lack of changes mean that it, and the associated gameplay experience, is growing stagnant. Dropping a single pebble (the new attack button) into the water once per 2 years is not going to cause enough disturbance to prevent the stagnation of the water, we need either a much larger pebble (eg big changes at expansion time) or pebbles to be dropped in far more often (eg updates every patch, and no I don't mean 'Dia increased by 5' kind of changes)