Again, Oda went out of his way here to constantly have Luffy be looked at as the small time in comparison here.
And im talking about Arc allies who join Luffy to fight against an arc antagonist not the vague alliances made in Impel Down and Marineford where defeating an enemy wasn’t even on the table.
Because we all know whoever is the final villain of Elbaf, the last hit is going to Luffy. So unless this villain is going to defeat someone magnitudes stronger just to get beat by Luffy, it’s an absolutely ridiculous concept