I guess Sanji legs aren't burning hot either.
And you call me a clown. Your post is another example of poor reading comprehensive skills.
The notes said dragons, as in plural and King attack isn't a real dragon. It's nothing but flames and Zoro already had the ability to cut flames prior to fighting King. It wouldn't make any sense to say slay if it was talking about King's attack.
Zoro's flying dragon blaze scared BM and Kaido. That tells us Zoro already had the power to cause Kaido significant damage before obtaining CoC and without need to use asura mode. His asura mode attack, while he's in a severely weakened and injured state, scarred Kaido. It's reasonable to believe and makes perfect sense an attack with overwhelming CoA and CoC haki can slay dragons like Kaido with one hit.
He's the thing you're missing. Kaido greatest power is his incredibly strong and durable body. That's the part of Kaido's power that Oda hypes up the most. If you have the power to defeat his durability there goes a huge part of the battle difficulty. Loki is not as durable as Kaido. Shamrock proved that. Attacks that are very effective against Kaido durable body will be even more effective against Loki's.