with the latest emphasis on how sanji is luffy's wings, it should be clear to everyone that luffy can't do everything by his own.
luffy suffering many 1v1 loses doesn't necessarily means he's gonna redeem himself with a 1v1 victory, it also means that he needs help.
He can't become PK just by winning a 1vs1 fight, he needs hiscrew to fight other crews/armies and to help him with everything outside of fighting. But way back to the Arlong Park arc, Luffy's SINGULAR skill is to beat the fuck out of the strongest guy in the other side, this has been drummed into us throughout the series. You want to cuck out the MAIN CHARACTER and belittle his ONE ROLE in the crew, so his subordinate looks better.
This is a shonen, Sanji is not aiming to be PK, Zoro is not aiming to be PK (and Mihawk not only admitted PK> WSS in Baratie, but reconfirmed there was a distance between him and oldbeard).
Luffy and Kaido are both aiming to be PK. This is personal, Kaido even threatened Luffy to say his dream in front of him. This is fundamental to Luffy's character.