@rerere If Kaido would have come down to face Kid, Law, Marco and the others. Luffy would be seen as ridiculous. Other people aren't always going to do things for him.
And BM would have been even more humiliated than she already is if in addition to having the strength to stand up, Kid and Law would have managed to fight Kaido again.
Kaido and Luffy is when the main battle of the arc for Luffy to prove that he will beat Kaido to legitimize his future status.
He had already had plenty of helpers on the roof. Everyone would have disputed Luffy's victory if he hadn't continued to do the last 2 rounds in 1v1 (chap 1026,1028,1037,1041,1042,1043,1044,1045,1046,1047,1048, 1049).