Just like he established Luffy/Kidd/Law are comparable? Same bounty?
Their rivalry is an ongoing Gag. They are never gonna fight in actuality to prove who is stronger, Just like Natsu/Gray, Naruto/Sasuke... were rivals outside of gags... one of them was always clearly superior.
Same goes for Shanks and Mihawk, one is always the stronger one.
Sanji had an entire arc to himself in WCI and Zoro still managed to out perform him.