I'm actually pretty sure Hachi being Arlong's #2 was a mistranslation.
And honestly the only times Zoro hasn't fought the #2 was for pretty good reasons. In Arlong Park he was nursing a wound from Mihawk that was stated to need 2 years to heal and was almost passing out while fighting Hachi (then Arlong hyped Zoro up for enduring with an injury as bad as his).
Then Thriller Bark he fought Ryuma (which introduced us to Wano) and fought Kuma after and got the awesome "Nothing Happened" scene.
So the people who think Sanji will fight King better get ready for Zoro to do some crazy shit against Kaido instead :cheers:
Not to mention that fighting style it was better to
Meaning... Kuroobi was martial artist... and Abasalom was invisible man (and both are NOT swordsmen) or fight with any blade...
While Hatchi and Ryuuma both were swordsmen... so logically... you give the swordsman to swordsman and the person who fights with their bodies to Sanji
But anyway... King does have a sword... while Queen although he does carry a sword... his fighhting style against Big Mom tells us he's more about his body than swords...
And although I do agree that King can fly and Zoro doesn't... Oda honestly does tend to make those fighters end up wanting to DIRECTLY clash with Zoro (which gives Zoro his chance to win)
Meaning..
Braham from Shandia is a great example.. instead of to continue fighting the same way he was doing and defeating Zoro with his flight ability and shiny guns... he was like an idiot wanted to confront Zoro's 36 pound pheonix...
So... King will do the same.. he will tire Zoro a lot with his flight... then get cocky.. then with Zoro's big attack.. King will be idiot enough to head straight for it head on.. which will result in his defeat.. I can already see it from miles LOL