Sure. Blackbeard can destroy the whole world with an earthquake, and there's nothing anybody could do about it. So, it would be more relevant to consider less overpowered cases. Besides, even in such a case the fish folk would be the ones better off. If Blackbeard destroyed the fishman island so deep underwater from the surface, he would at the same time cause such widespread damage that multiple human islands would be wiped out. So, the fishmen would need to swim somewhere else to build a new home, but lots of human countries would become nothing but footnotes in history books, all of their citizens dead.