zoro wont kill kaido....alone.
most of the crew will work together to kill kaido. its not "zoro kills kaido" as much as it will be "the straw hats kill kaido" in a combination attack like vs oars or kuma. everyone on the crew as far as i know understands that some people are so bad they have to be killed to be stopped. even chopper.
chopper sees big mom asleep on the beach and immediately draws a sword and says he's going to kill her. this was a scene in the manga as well, its canon. he also says
"she's the same as kaido." meaning, kaido also needs to die and he's ready to do it. and this is the ship's doctor. robin is an assassin. jimbei is a mob boss. franky is a gangster. brook is a military man. usopp is a sniper who names all of his techniques "instant kill" attacks. nami is a nice girl but she'd kill if it came down to her or the other guy. sanji is a gentleman but he was ready to kill absalom before, why not kaido. luffy literally promised momo he'd kill kaido if i remember right.
they're all ready. zoro is just delivering the finishing blow.