Tbf Zoro not seeing Kaido was believable just judging by Oda's historical arcs of Luffy facing the main villain and Zoro facing the subordinate
It's one of the first arcs where Oda really went all out with Zoro by having him fight the main villain alongside his captain before ultimately going through the same routine of Luffy eventually following through and Zoro fighting his strongest subordinate
With that said, the hints were there that Zoro could fight Kaido with the mythical dragon theories, his link to Wano, him getting Oden's enma(which could scar Kaido) and so on, which is why i think both sides of the coins had believable reasons
Them fighting the commanders was always guaranteed tho