Luffy's final showdown with Sir Crocodile still throws One Piece fans for a loop, but there's a simple answer.

Garp, known for Haki & training, will be eclipsed by Luffy post-Elbaf arc. Mihawk, Big Mom, Five Elders, Sakazuki, and Kaido, ...

King And Queen never fought Luffy during the Raid on Onigashima and faced Zoro and Sanji instead. Luffy and Eustass Kid never had a major fight despite being rivals and allies against common enemies.