Luffy wins High Diff. If Luffy didn’t have FS, I would say this maybe a extreme diff toss up, but he does.
Zoro with Enma has aCoA, he can cut the horn off of onigashima & a city size mountain with his Haki, can damage Kaido a decent but with his Ashura attack & has a crazy high ceiling of endurance & stamina.
Luffy before awakening his aCoC, had FS & ACoA. He was able to casually damage Kaido with his Red rock & Gear 4 attacks; & Even tank Boro breathes. This Luffy gassed out quick after Gear 4, and got beat by Kaido’s hybrid form quickly.
So like I said before; Zoro at times in the arc is really close to Luffy; & this is the time. Zoro has enough attack power & endurance to damage & hurt Luffy while receiving damage as well. IMO it kinda boils down to will power, & that’s where Luffy wins. Because Zoro’s strongest attacks are deadlier than Luffy’s best techniques.