I think you'd be surprised by how much more could work if simply removed of certain arbitrary obstacles.
Take the "Bene lag" for instance. It actually was unique in how long it took to take effect, specifically because it didn't actually apply the heal until after its animation had completed, whereas others may apply it at the start of the animation. But, shit like that doesn't require a change in netcode to fix. They just need to not purposely delay, for thematic "grand heal" purposes, an emergency action's activation to... well after/longer than the cases it'd otherwise best be used for.
That said, I do agree that a HUGE number of opportunities could be opened up for healers through broader (or, more underlying) improvements and little quirks to better leverage them. Pre-healing, for instance, is kind of absurdly fun to me -- to hit an ally with the very end of a precisely timed preemptive cast and instantly follow it up with another banked instant cast to bounce their health back up the moment a TB had reduced them to critical (rather than just... oGCDing it). And, we were able to support that already -- we just had it covered up too much to matter. These days, I'd also love to see manipulable (diminishing-per-bounce) chain-heals, stored or time-locked heals, life-linking, and other fun little mechanics becomes available to our healing roster. Yeah, our netcode may get in the way of some of those somewhat, but I don't think it'd cripple them.
I don't think we need anything particularly wonky to do that. We just need to stop making AoEs so damn OP.It'd be cool to have actual 'triage' situations, but the reason it works better in, say, WOW, is that AOE healing is not plentiful. It's either kinda weak but spammable, or has some internal CD like WildGrowth, Circle of Healing, Dream Breath, Spiritbloom, PowerWord:Radiance, etc. In order to have a similar environment here, Medica and it's equivalents would need to have a 10s CD at minimum.
Maybe they could do it with a hacky workaround though, some kind of debuff that means 'only single target healing affects this player for X seconds', then have it applied to, idk, 2 DPS while they get clapped by adds.
Heck, the most fundamental difference between XIV AoE heals and WoW's isn't that WoW's are tuned more weakly, but rather that AoEs don't have to be simultaneously useful for a half-sized party and a full-sized party.
You can make up for that light party / full party wonkiness quite easily, though, just by having a portion of the AoE's potency be split among all receivers. The AoEs' total potency would still increase with party count, but not so steeply as to make all else irrelevant.