But is he defeating him? Thats the question being discussed here. The argument was always whether or not Saturn is an endgame antagonist or simply an arc based one, and the fact that all 5 Gorosei are here now kind of shoots the prospect in the foot of him losing here.
The only reason any of us are saying Kizaru is because Luffy reasonably gets wins every arc, so if its not a Gorosei (maybe it still is, im not saying it's "impossible"), the Admiral is really the only other choice here.