Just one additional Damage Spell could do a lot - Mushrooms and WHMs

[Eisi]

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%.

It doesn't need to be needed it just needs to not be a dps loss up to a certain point.

I would make it so and then check how players react. Will they still only ogcd heal or will they organically switch things up just because they can? What is more fun to them? Then I would dial back on the OGCDs if players enjoy GCD healing in a damage neutral fashion.

Fun is really the most important part, if players can optimize the fun out of the experience, they will. So you wanna make fun optimal.