Kid who has CoA was confused as to why Luffy was hurting Kaido with punches alone, it is safe to say that regular CoA just doesn't work even if you want to dismiss all the training Luffy specifically went through to hurt Kaido
Kiku having a higher grade of CoA doesn't make her stronger than Kat, just like Enel having a higher grade of CoO doesn't make him stronger than a guy like Law