What are the reasons for nobody else taking over Kizaru, though? I mean, Zoro + Sanji + Jinbei + potentially Nami/Chopper/Ussop should be enough to at least stall Kizaru whilst Luffy fights Saturn. Its possible that even through that Kizaru's attention will be on Luffy V Saturn, kind of like how Mihawk's attention was on Luffy whilst he was fighting Vista. The way I see it, Kizaru clearly has the potential to be good. His wavering and his symbolised by "unclear justice". Everything points towards the battle of good and evil in this arc being Luffy-good and Saturn-evil. Saturn is the absolute evil of this arc after all. I don't think its necessary for Kizaru to get packed up done and dusted this arc because narratively, Saturn needs to fall, in order for BB's plan and what Devon did to not be completely useless. We can safely exclude anybody else introduced as BB Pirates - they already TP'ed away and said their mission is complete, possible they will encounter some Straw Hats or somebody on the way though since they couldn't TP directly off the island. Kuma - he had his moment, Saturn regenned from it and now Kuma is being carried around and unable to fight.
I can see that at least for the while being, Luffy will still fight Kizaru since they were standing off against each other last chapter to protect PV but it'll be very brief since if the Shanks dudes hints is to be believed, then it indicates Saturn, is obviously back and doing a big thing within less then a chapter. Point is, the fight wasn't really protracted at all. They could've been staring off and shit talking each other for the moment Saturn was making his way back.
Imo, Saturn V Luffy is significantly more important and narratively relevant then Luffy V Kizaru. I do not believe Kizaru can represent a challenge bigger then Kaido and its not just admiral hatred or whatever, but the first fight between Luffy and Kaido was Luffy getting 1 shotted. The first fight between Kizaru and Luffy you already know.
