King fight is the same as the Mr 1 fight. One might consider them "extreme diff" because he DID have to push himself to his limits in order to beat them. What he lacked was "the ability to hurt them". As soon as he can hurt them its his win, but because him being able to do that was up in the air until the last chapter of the fight, its a difficult fight
If Alabasta Zoro fought Mr 1 after their first fight, itd be a low diff, maybe even neg diff encounter. But that doesn't erase the fact the fight WAS extreme diff. Same here