I'd say we only saw a little of Ace, his potential is definitely greater than that of Dark King Rayleigh. Sad to say, he died before he could reach his greatest form. Even aged Rayleigh can be bothersome for Ace, if not too much. From watching a glimpse of Rayleigh vs Kizaru. I'd say Rayleigh wins, though he has aged, he's still deadly. If someone can show that Ace could use a high level of CoA, I'd say he wins, but that is not the case.