Luffy was using hakiless hits on Kaido too then, cause his hand wasn't black and there were lightnings missing.
The most obvious and reasonable assumption is that they are using haki all the time, and lightning is shown when Oda wants to especially highlight the haki usage, instead of assuming they are fighting literally turning off the haki.
But ultimately, we can't conclude shit cause Oda is way too inconsistent with haki.
Say what you want, but I know that even you don't really think it was hakiless attacks and lying for agendas. Keep coping cause deep down you too know Kizaru stocks are down here.
Dude he can't move for at least a few minutes, Kizaru is done at least as far as this battle is concerned.
And it took one clean hit to do it.