Luffy, with help from others at the beginning of the battle or BM interjecting at the perfect time. The only exception to this is if the "Ace" exists and becomes Luffy's actual battle (which I'm doubting now but who knows). If this happens, then Kaido's fall isn't happening at Wano or it can be a full blown, concentrated effort by many people.
Reason I say this is because Luffy is always warranted a non-warmup 1v1 fight every arc. He is the main character, Oda will draw his 10-15 chapter fight with someone. It always happens. If its not Kaido, then it will be the "Ace" because it has to be someone stronger than Zoro's opponent (who is very likely King). If there is no "Ace", then its Kaido.
One or the other, Oda hasn't changed this method in 20 years, he's not going to let someone else outshine Luffy.