I see people still trying to make it sound like "ACoC" is some next level evolution of "base CoC" but this is nonsense.
Luffy, Sanji, Zoro all instantly used ACoC. There was 0 training. When it's shown time and time again that having "base CoC" is the main requirement, especially in the case of Zoro and Sanji, it just shows that people only see it this way because of Luffy's weird Haki progression.
Luffy did the hard part first: unlock CoC, but he still had basic hardening CoA. He couldn't do the coating technique. But the coating technique is fairly trivial. Kinemon can do it. Kiku can do it. So can Hyogoro and Marigold.
Luffy called it "advanced" because he was thinking of Rayleigh's ACoA. This is where the confusions stems from. You don't need ACoA to do coating. Hyogoro explained that ACoA is just a more powerful evolution of coating. Yamato showed this.
Conclusion: Luffy just had a weird path where he had fully unlocked CoC, and then he learned coating. But this is very abnormal within One Piece. as even relative minnows can do coating.
This was obviously because Oda hadn't fleshed out "ACoC" up until the end of Wano. Even Kaido and Big Mom did not show it up at the start of Wano.
0 visual evidence of "ACoC" here. And the worst part is the VIZ translation where Kaido made it seem like only Top Tiers can use it, just made some people double down. In reality all Kaido said is "only a handful of strong people can do it" not "only the very strongest can do it".