Why cant you agree with that when the strongest of them all, Kaido himself, said that Zoro belongs to a handful of the very strongest?
Or when he said that with Zoro's strength on his side, he could conquer the world?
While aCoC is ability of handful very strongest, Zoro's King of Hell is even a step above that.
I dont know how anyone can still doubt Zoro's strength. The guy is built to win, not to fail like his captain does countless times per fight.