Did something like this happen in Wukong legends?
Or in some ancient japanese myth?
Originally, Wukong was the strongest under the heavens and essentially the main enemy of heaven and a dictator. In a way, he was an existence similar to Kaido.
Before the events of Journey to the West, Buddha beat him and trapped him under an enormous mountain, the 5 phases mountain, which represents the weight of Wukong's responsibility for what he'd done and what he was trying to do.
Of course, what greater representation of the responsibility Kaido has for his evils, than the huge floating Island which he picked up, representing his rule, and which he was going to drop on the capital?
And obviously a mountain alone wont stop Kaido, so adding on to it, to further restrain him as a devil fruit user, and since it's an Island, he should also be partially trapped underwater as well. It would even add significance to the fact that Kaido's Dragon fruit is categorized as a fish.