Zoro vs Mihawk IS Happening, just not when Luffy fights Blackbeard. Nor if Luffy fights Akainu, because Fuji/Ryo exists.
There are really only two places where it makes sense:
- Shanks: Because Beckman actually is not a blade user whatsoever (though yes,that can still happen), and Shanks and Mihawk are obviously tied together.
- Im: If the Monk Gorosei is not that strong and/or Mihawk is somehow associate to the God's Knights (which would be weird but there are weirder ideas)
Tldr theres a lot we dont know, but clearly Mihawk is not associating with Akainu and Blackbeard of all people.