Oda has made it clear that Kaido is #1 on the list since his 796. That's why Luffy is fighting him now.
However, that doesn't guarantee he will win every 1 v. 1. If you think of their stats like
Kaido - 80 attack 90 defence
Mihawk - 95 attack 50 defence
Kaido's average is 85 while Mihawk's 72.5, but Mihawk can still beat him.
Oden was like this. Kaido's defence >>> Oden's defence, and we saw what happened
A pirate's strength is best measured in a war setting, fighting multiple people, like Whitebeard in Marineford. In a pirate war, Kaido > Mihawk, because of his skin and the ability to tolerate attacks like this
Mihawk can't handle those ^ attacks. But like Oden, that doesn't mean he can't beat Kaido 1 v. 1.