But thats what needs to happen. No one can hurt Kaido without using ACoC. So Momo would need it himself to hurt Kaido. Thats what makes the writing bad, if Momo ends up hurting Kaido.
There are legends about Dragons being able to bypass other dragons scales and hurt them
Momo can be a special case in that regard according to myths… that’s how I see it…
Also, just for the info, you can hurt Kaido without CoC, but the damage will not last, he will heal…
We saw scabbards hurt him with ACoA, but the damage won’t last because they are not ACoC…
Also, fire can hurt him, but it should be strong fire… which was shown with Raizo returning his boro breath on him…. So I would say a mera mera user can actually land hurtful blows on him… or magma…etc!
He MIGHT be vulnerable to other elements but we have yet to see