That wouldn't be necessary because I do not think when one claims that X character's attack is island level or size of an island, they are not talking about a tiny piece of land surrounded by a body of water..... which is what the dictionary definition of an island would cover.
Obviously, Luffy's fist doesn't exactly have to be as large as Onigashima to be island sized. Marineford is island sized - albeit being a small island - but it is not even as big as the skull. Luffy's fist could easily engulf: Marineford, Cacao Island and several other islands of similar size.
But for one piece, when some claim "island level" it should span several dozen kilometers
I don't know what you're starting to do with this kind of information but the manga basically showed us that the fist is meant - both in feat and statement - to be comparable to the island. A few inconsistent drawings do not change this fact.
Kaido regenning has happened throughout the raid, whether it be visibly through the scabbards and Zoro's wounds closing instantaneously, or Luffy saying that his internal destruction damage is too shallow to do lasting damage to Kaido.
Luffy merely stated his ACoA attacks were too shallow, which wasn't the issue with his CoC Power-Up.
Luffy recovered FROM DEATH due to his mythical Zoan awakening, and has taken multiple powerful blows since, you are for some reason assuming Kaido's HP bar has remained static while Luffy recovered from a worse injury???
But since you're mentioning this one, we literally have a panel of G5 Luffy recovering very quickly. How does it help your case?
Kaido was panting in consecutive panels and going all out in his swole mode (aside from trump card non physical fire attack he is using now).
Also, Kaido was panting in few panels but kept on tanking more hits. If he takes the God fist as well, you can forget the idea of another OKG knocking him out.
G4 is susceptible to having air knocked out, and Luffy was in a worse condition having just been blasted to shit from a boro breath point blank.
Again, one attack knocked Kaido to the ground whilst quickly recovering and counterattacking Luffy - who was speedblitzed! - meanwhile, the other attack nearly knocked Luffy out AGAIN.
Luffy had the belief that his second blow HAD A CHANCE.
Luffy came into this final 1vs1 much more nerfed than Kaido, and still pushed him to that extent.