Luffy is the one who "nerfed" Kaido so saying that Luffy is fighting nerfed Kaido is not genuine
Luffy, Zoro, Kidd, Killer, Law, Yamato, Neko, Inu, Izo, Kawamatsu, Kiku, Kinemon, Denjiro, Raizo (so Kaido himself with the Boro Breath)
And he was lifting Onigashima
Aside from Kaido, Luffy was injured by Apoo, Ulti and took one attack from Big Mom
He had rest and eated a lot of food
I would never call it a fair fight