I think it's gonna end being a tag team.
There's just a few things about the characters that neither of them can deal with that easily alone.
So Zoro can cut Queen's metal arm / tail, and Sanji can follow King up in the sky and trade fire kicks.
But Sanji won't deal well with King's swordsmanship, so Zoro will take care of that, same way Zoro can't deal too well too many projectiles from Queen, but Sanji can deal with those using the Raid Suit and his shield cape.
It has potential to be one of the coolest fights in the series.