Im.not sure what you said about ryou.d
During the udon, luffy just tried to learn how to use ryou. First stage , he used ryou as a advanced coa, and then he realized that kaido using with coc, and then he added coc coating. I guess you don't understand what ryou is.
Even though zoro don't know hot to use coc right now, thanks to enma , his attack made advanced coc attack.
You are the one that doesn't understand Ryou.
Ryou is simple basic haki applied externally of your body. Everyone at Amazon Lily was using Ryou. Sentomaru was using Ryou. Rayleigh against the Elephant was using Ryou. Hyogoro was using it.
Adv CoA is internal damage, both Luffy and Rayleigh was using it when breaking collars. Hyogoro himself stated that when Luffy breaking collars "this is way more advanced than the ryou I wanted to teach you", or something like this.
Luffy never used Ryou he went straight forward to Adv CoA(internal damage). Ryou is not internal damage, is simply barrier.
Zoro is the one using Ryou since Mr 1 fight(breath of all things just like Hyogoro said in his explanation, same explanation of Zoro's teacher in his flashback).