Yes Lilies being DPS neutral would cut down on the need for oGCD's when there's big downtime between the damage you're taking, but in some fights and scenarios, the fact that WHM has pretty much no oGCD's means that they have a hard time outputting the amount of healing needed in a short amount of time. For instance, the final Channeling overflow in P2S paired with coherence, you can put down bell but if you don't get a fast arrow you don't take any damage to trigger your bell heal until the biggest chunk of damage is already coming at you, and because of how spread out everyone is before grouping up, Cure 3 is likely to miss people running for the stack so you're pretty much forced to Medica or Medica II and then Afflatus Rapture and then try and see if anyone needs any extra single target help with Tetra or Benison in the split second before the massive stack damage goes off. My point is, for what is supposed to be the best straight up HEAL healer, they even struggle with this because there's really not much they can do while WHM's wait for their GCD to tick over. WHM's are alright at the cleanup after if you make them damage neutral with the blood lily, but their lack of oGCD healing makes their effectiveness in the big moments pretty weak because they really don't have much to supplement their GCD healing.

As far as homogenization goes, I really don't understand how Collective Unconsciousness and Earthly Star have anything to do with an Afflatus Rapture oGCD because literally none of these skills are alike at all besides the fact that they heal. One's a regen, one's essentially a burst bubble and the other is just a heal. Your argument for that makes no sense to me.