Oda wrote Luffy saying that what he can do for his crew that noone else can is beating the main villain (Arlong, in this case). He also had Luffy beating the Shichibukai, not his subordinate; had him beating the 4000 doriki guy who would go and kill the whole crew if not stopped right there, not his 2200 subaltern; and now has him making Kaido enjoy a fight, the same Kaido who compared him with other top fighters with just one punch and was introduced as a person bored with the world and borderline depressed.
This isn't matchup nor PIS. This is the author telling you that Luffy and Zoro aren't relative to each other, and readers complicating his simple work with useless overanalysis. I don't know if Luffy is going to be on some GodTier (whatever that means), but what I know is that, if there's a character with the potential to be there, that's Luffy indeed.
This whole story is about him. Zoro is secondary.