Further to Semi's point, remember that recently Sebazy tried doing an EX roulette with just GCD healing sources as WHM and still got a 94 on damage. I'd estimate that, to make 'GCD healing incentivized/needed' you'd have to remove EVERY OGCD we currently have, and ALSO reduce every AOE GCD heal's effectiveness by roughly 30%. And who would be up for a change that says 'oh yeh btw, we made it so that Cure3 is now 400p, Rapture is back down to 300, and now you don't have Bene, Tetra, Asylum, Benison, and Assize is just damage'. You'd get to keep Aquaveil and Temperance though, I guess since they're mitigations rather than heal/shield

It's such an insane level of overhaul required to get 'just increase how much we have to heal' to actually work as a design choice