There's no evidence that Luffy has enough stamina to inflict enough damage on a fresh Kaido.
One ACoC G5 Punch can atleast equal half of it if we're being conservative. And we know Luffy can spam ACoC in base, and we also know Luffy can fight with a Drunk Kaidou with gear stacking (technically base at this point). 1 min tops and he is able to replicate whatever superficial damage Kaidou suffered prior to fighting fully realized Luffy.
Luffy being at his current lvl able to do meaningful damage from the start of the fight, would be a lot worse for Kaidou than those "15 characters" doing shallow damage. This means right off the jump Kaidou has to eat AdCoA + AdCoC.