There is nothing wrong in using several angles and perspectives to showcase how Luffy's giant fist is comparable to Onigashima in fact, as well as Fire Dragon Kaido. Considering Yamato's statement "He's going to punch through the island", why is this one panel last chapter unreliable to be used?
As I said, with the recent panels, it really got more difficult to scale the punch accordingly. Sure, we can wait for the full chapter or the next one but with the statement last chapter, there's actually no doubt that the sheer size of the fist is comparable to Onigashima, even if it ends up being comparable with the skull in size.