Luffy got hungry versus Katakuri and wasn't able to use Future Sight in his Snakeman form. In fact he started to miss a lot of punches after that statement.
Doesn't matter if Zoro's attack didn't had black lightning. It scarred Kaido. Anything without CoC coating is too shallow on him. Oden attack that scarred him was with CoC coating so to Zoro also scar him it has to be CoC coating attack.