1º Solo 1v1 and defeating Kaido, is living proof that ZORO would be> Kaido, he would be canonically above.
2º But when he needs the help of several people, it ends.
3º There will be situations that if it were 1x1, Kaido would have ended the fight, because he has no one else to hinder or help, protect, save.
4º There will be times that you will only be able to attack and hit because of the openings created by the other characters, while 1v1 this would not be possible or easy to do.
5º Nobody, absolutely nobody, will be able to replicate the achievements that Kaido made alone, zoro, luffy, kid, law. None of them.
Why ?
Let's use Law as an argument, Law would do 1v9 against: Neko and INU sulongs, + Kyoshiro, Ashura, Kawamatsu, O-kiku, Kinemon, Izou?
And after that go to Luffy and zoro, kid, killer, sanji, jimbei and any other opponent that kaido will face?
Would Law have that ability? All this alone? No, that's why nobody will come out stronger than KAIDO, kaido is sealed as the best 1v1 of the work.