I mean, Lilies are GCD heals. Straight up. Saying they're not is saying Regen isn't a GCD heal. They are spells, they are on the GCD.
The distinction is incredibly important in how a spell or ability is utilized. It's also important for +healing magic potency effects, what benefits from it and what doesn't. It even means they're not usable while silenced, and it means they will not bypass -healing received mechanics in earlier content, something tetra, bene, assize, and asylum CAN do.
It is not trifling semantics to separate oGCDs from GCDs. That they are not spammable does not change this.
Also, mentioning PI as an oGCD heal is kinda misleading. It's more of an oGCD buff to AoE GCD heals. Doesn't do you any good if you're not following it up with AoE GCD.
Hitting PI while a tank is on the brink of death will do you very little good. It will make Medica II stronger than Cure II over the duration in this situation - which also takes 0.5s longer to cast and forces a full clip if you're oGCDing after. If the tank is dying it's a little late for you to be applying HoTs.
Edit: I suppose it would actually make Cure III > Cure II on a tank in this very specific case by +50 potency, though. So there's that. I've certainly used PI Cure 3 in 2-tank multi-hit tankbuster scenarios as an oh-crap-cohealer's-dead button. I actually wish PI affected all our GCD healing, I see little reason why it shouldn't.
I get that we're poking fun at the hypothetical situation that has flaws already, but might as well be as accurate as possible with our responses.