Why would Ulquiorra's statement mean two different things depending on the user? Why would Ulquiorra's Gran Rey Cero pulverize in his base form and vaporize in his released form?
Because he gets stronger when he releases. We don't assume that just because a Cero has shown vaporization for one character, it must be the same for every character.
The amount of speculation that goes into making this work is what leads me to be against this method.
It's quite literally 0 speculation regarding whether GRC vaporizes or not. GRC > CO > Cero -> Res Ulq's CO vaporizes -> Res Ulq's GRC > Res Ulq's CO -> Res Ulq's GRC vaporizes as it is more potent than his CO -> anyone who scales to or above Res Ulq follows that same logic, anyone below Res Ulq has no concrete evidence that their GRC can vaporize.
ofc I'd love for all of them to apply vaporization
Personally, I don't think we have enough context to make a good enough judgement of this.
If we had a statement like "There'd by no trace of Las Noches left" or "The Gran Rey Cero could vaporize the entire structure" then those are better straightforward statements.
We can use deductive reasoning -> Res Ulq's CO vaporized a massive chunk of LN -> GRC is a more impressive Cero via statements from the manga and databook -> GRC can destroy all of LN -> insert my calc here. Again you're being nitpicky about your statements just like Gremmy's meteor, the whole "he doesn't tell us he'd vaporize 96.72563% of this structure, therefore we cannot calc it" is very poor reasoning.
It's super simple -> Res Ulq's CO can vaporize ~1/4 of LN (eyeballing it) -> GRC > CO -> GRC can destroy all of LN. Well if Res Ulq's CO can vape a sizeable chunk of LN, but his GRC (which is a stronger Cero) can destroy all of LN, logic reasons that it'd vape the entire castle.
Again though, vaporizing 1/5 of Las Noches doesn't guarantee it would be able to vaporize the whole thing. Ulquiorra's statement did not indicate there would be nothing left at all, or that vaporization of the entire structure would happen.
It seems pretty obvious from context that there'd be large-scale destruction if you fired a large-scale attack from the inside of the dome. But speculating further than that seems unwarranted.
Pretty much what I just said above. However, as you even imply yourself, CO being able to destroy a massive portion and being less impressive than GRC does in fact reason that GRC would be destruction on the scale of LN itself.
The next question that begs is, what methods of destruction? To which if CO, a less potent Cero can vaporize, then GRC should be able to as well (for characters >= Res Ulq). Next I scale down to pulverization for those who don't scale to Res Ulq, as it is the beneath that in the totem.
I mentioned up above that I don't feel so strongly about this point, but if we wanted to extrapolate what would happen, then Grimmjow would presumably have punctured a hole in the dome. He would have "destroyed Las Noches" by damaging its structure. But he wouldn't have caused some kind of explosion that blows up the whole dome, and he wouldn't have vaporized/pulverized the entire structure.
Grimmjow not destroying anything just means Ichigo blocked the brunt of the attack. As you said, it's not a strong point, because the attack never goes off, it's blocked. Thus this isn't an anti-feat at all.
EDIT: I am interested in seeing IMade's thoughts, and for any other staff member's thoughts.
Same