Sanji defeating Kizaru is at zero, not even if Kizaru holds back a lot.
And the reason is simple, dude took off Luffy second strongest move, with G5+CoA+adv CoC...
Sanji even with IJ does not have the AP to be on that lvl, pulling out AP on the same lvl as Luffy did would make Sanji a legit top tier, meaning he having skills who are in same category as Luffy strongest second G5(for now) attack...
If Kizaru really goes down, it is either Luffy himself or a tag team between Zoro+Sanji vs Kizaru.
But since Lucci vs Zoro is still continue, i doubt we gonna get any tag team battle.
I think this arc is a parallel to SA, means not just Luffy, but the entire strawhats will show that they grow up.
Luffy when he encounter Kizaru: WE got 100 times stronger"
Kizaru this chapter: "I want to see how much you guys grow".
It clear that Oda plan to let all strawhats shine this arc.
Luffy will either defeat Kizaru or Saturn
Sanji,Franky,Usopp,Nami,Chopper and Brook will also shine vs VA and navy
Zoro will defeat Lucci and show that not just Luffy is a beast in the crew.
Jinbe and Robin will care on Buster call, Jinbe in sea together with Robin will stop the buster call...
Who ever face the ancient Robot, this one will be not defeated this arc.
Means if the ancient Robot face Kizaru>I doubt Kizaru getting defeated this arc. Since Luffy will face Saturn and defeat him.
If the ancient Robot fights Saturn and stall him, im pretty sure Luffy will beat awakened Kizaru.
Oda teased a lot this arc, I assume soon Kizaru will show his true power, use awakening and test all strawhats.
Kizaru wont change the sides, not yet.
Otherwise it would clearly change the balance of this arc, Luffy and co would be to much for Saturn and the navy if Kizaru joins them now together with the ancient robot.