Luffy will high diff, King. I can't see Luffy defeating King without struggling as Zoro did. This is a fact.
In fact, if King fights Kaido, it would be a tough fight for Kaido and he will not beat King easily. The fight might last a day and Kaido will be seriously injured.
OP fans have wrongly understood power scaling in OP. They think a Yonko can one-shot a commander, low diff or mid diff LOOL
Do you think if Luffy fights Zoro or Roger fights Rayleigh they will mid diff them? A big LOL to that logic.
Luffy vs Zoro, Rayleigh vs Roger, or King vs Kaido will end up in high diff.