Its not that Zoro not being allowed, its how Luffy should be the one defeating Kaidou while no one else can. And also its the clash for PK instead of WSS, so Zoro fighting Kaidou in a full blown battle feels like Luffy fighting Mihawk in a full blown battle with the intention of defeating him. It feels interfering.
Anyway Zoro rooted for Luffy after experiencing WSC and seeing Luffy's CoC Coating, he stated Luffy will win, giving the fight to Luffy who is deserving. He rooted for Luffy instead of saying "i'm gonna come back and ZKK etc". If ZKK will happen, it means Luffy doesn't even need to fight Kaidou. Just send Zoro to do that, apparently he can do ZKK so Luffy can just sit back and relax. He has so much nothing to do, he can just fight and defeat Imu in the same arc lol thats what i felt.