Plot armor aside, pre-nerf Katakuri beats that version of Luffy. He only beat Crocodile because Water > Sand. Willpower didn’t have anything to do with it.
I always took what he said literally as fuck. Haven’t read/watched DB in a while but if I remember right King Kai said if your body isn’t strong enough to handle the boost it could kill you. That’s why he told him not to go over X amount of times during his fight with Vegeta.
I’m assuming pre and post is referring to absorbing Goku’s KMHMH? If so I put him around Frieza after absorption due to the fact that every villain is always relative/stronger than the previous in order to be a threat in every series.
For some reason I can’t quote ahill, but you’re talking about CoA haki. Just adding armament to your sword and having a real black blade isn’t the same thing.