Serious question gets a serious answer: the dialogue from Saturn supports Kizaru's current "issue".
- Saturn says he is "unusually slow this mission"
- This is because he is conflicted with the mission itself (VP, Sentoumaru, Bonney, etc).
- He spent the last 4 chapters barely fighting Luffy and instead trying to zap VP.
- Both he and Luffy are fridged for the sole reason of progressing the plot
Once Saturn or something else alleviates Kizaru's of his "burden" and allows him to fight Luffy seriously, then he will. The whole point is that it took Luffy 4 chapters to land 1 clean hit on Kizaru. Can he do it again if Kizaru is fully focused on him?
So no, its not a battle of endurance like with Kaido. Luffy would actually need to be able to hit the Admiral properly and knock him out to win. He didnt even KO Kizaru here, and he was entirely vulnerable to Saturn.
These are things people have to consider going forward, its right there in the dialogue.