Kaido fought so far in a serious battle:
9Scabbards+5Supernova+Luffy alone+Yamato alone+again Luffy and Momo for hours. He took so many attacks, fighting non stop, Luffy was defeated two times already. In the firsttime when Boundman fall off and Dragon Kaido eat him(saved by Zoro), second time when he got knocked out from the island even thought got adv CoC as powerup only to eat food and comeback.
Luffy got knocked out twice, he only face Kaido while Kaido non stop eating attacks from 16 different people, let be fair. I understand the hype for Luffy and he really doing great job, but Kaido is so far better in terms of feats, I doubt that Luffy would be up after facing Kaido,9Scabbards,Yamato,4 Supernova and eating lot of attacks.
Current Luffy is for sure a mid top tier and pretty op, he will also soon show a new powerup, makes him a admiral lvl character. But let not forget the fact that Kaido is several injuried after facing sooo many characters...