I already have Luffy > Kizaru and I don't see Kizaru being defeated at this stage of the story, do you?
Yes...I do lol. This is literally the perfect time for Luffy to defeat someone like Kizaru in a shorter arc.
I've talked about this at length. Many of OPs villains post Wano may be more like Pre-TS. Side grades and not complete upgrades from the last villain.
Kizaru isn't tankier or literally stronger than Kaido, but his powers could throw Luffy Off his game completely if he hasn't mastered FS yet, which the story had never suggested that being the case.
Kizaru has also hit and insulted Luffy more than he has to anyone else. There's actual beef there from Marineford, second only to Akainu.
If Kuma shows up, that is entirely going to be Zoro's focus considering their history (whether they fight directly or not is a different story).