At this point this is complete headcanon.
Luffy said hello to Kizaru with advCoC, uses FS with Snakeman, is in his peak form G5 which is draining him, and is shown using advCoC when he landed for the first time this fight.
Luffy is throwing the entire kitchen sink, and he's exhausted. Sure he can power through it with sheer willpower, but that's where we are at rn.
That's not he issue alone, anything below G5 looking like chop liver is. Hopefully I'm wrong, as I don't want G4 and below to become useless, I thought we were past that stage when he could go toe to toe with Kaidou without even G4. So maybe this is just a Kizaru exclusive thing.
Which shows you how big of a problem Kizaru is.