I've explained this, but I don't necessarily think One Piece does "powerscaling" well or the same way other Shonen logically do.
Pre-TS is chock full of circumstantial victories for Luffy (i.e. blood and water for Croc, Rubber for Enel), both of which could be have been adetriment to Lucci in Enies Lobby if they fought him. Then, all 3 probably could have beaten Moria without his Oars nonsense. It's basically like side-grade scaling, each villain posed different threats for the MC.
After the last 10 years of clear upgrades in villains (to Doffy to Kata to Kaido, Hody and Caesar were out if their league), I think the series is heading back into this territory, where villains have different advantages.
Kizaru probably isn't nearly as tank as Kaido or can dish out the same haki directly, but because of his broken powers, Luffy could be in trouble from the speed and weight of the kicks alone.
That's my 2 cents on that. If he can't keep up Kizaru like he couldn't with Kata at first, then we are looking at something interesting imo.