realize you said he went back up just to go after Luffy's crew but not Luffy himself why is that?
Yeah no shit kizaru is a tier above of an opponent compare to rob Lucci that much is obvious. So what it took more effort from kizaru never said kizaru was weak but to Luffy it was all the same in the end.
maybe this is hard for you to comprehend so let me example it slowly. Kaido face of the scabbards who all manage hurt him by the way and also put him down for a bit in his dragon form remember that scene?
Then afterwards he have to face the five supernovas granted he had help but they also managed to damaged then after that he was facing Yamato who also got a bit of damage from her. Point is kaido has being using a lot of stamina and has been taking accumulated amount of damage throughout the entire war and it against strong people too. I'll admit Luffy was in a worse state but kaido was in a worse situation because unlike Luffy he doesn't have time to ever recover his stamina.