1. Kaido is not Zoro nor everyone, that’s a very old statement you have to pull out. Zoro took great damage from Mihawk, Kaido hasn’t taken any great damage. It’s all accumulative damage, his endurance is the thing that’s weakened him. Many instances have shown that emotions play a role in battles, and actually serve as boosts. Luffy has bested most of his opponents so far after a dragged down fight, and no one shows their strongest moves at beginning of fights. Only in desperate scenarios, so Kaido will fall this arc after a dragged down fight, and he’ll show his strongest moves. No non-top tier level opponents for Kaido can even push him that far because they don’t have the damage to compete even when Kaido’s exhausted.
2. Potency of CoC is not reflected on your current state. That statement by Ray means your CoC grows stronger based on your overall strength. A 1 hp Kaido can still deal massive damage with CoC, he’d probably just die because of running out of haki.