Kid, Law, Killer, X-drake, Hawkins, Urouge, Capone, their haki knowledge is limited, they didn't have the pirate king's right arm and strongest swordsman training them for 2 consecutive years, when Luffy finished his training, he already knew of Ryou's existence, and Fs, he knew he could evolve his HAKI in intense battles, in both cases he always had a flashback of Rayleigh, when he was learning Ryou and when he was learning FS, the last thing that luffy was missing and that he didn't know was ACOC, that's different from KID and the rest (SNS) who spent 2 years in the new world without doing anything relevant, without any teacher, that's a fact , so realistic that KID confirms, "Can you hurt Kaido with physical blows?!"
Unlike Luffy, Kid and Law had to max both their DF, not their HAKI, as their HAKI information is very limited, yamato was beaten by kaidou since he was a child, he logically at some point in history he learned from Kaidou how to use advanced COC, and when he became strong enough to do so.
So what is most convincing to you:
1st - Luffy after taking lessons for 2 years on Haki and using his knowledge to advance his HAKI and get FS and Ryou.
2nd - Law and Kid and the rest of the (SNS) who didn't have a teacher learn FS and Ryou at the same time as Luffy?
The second option would show that training Luffy and Zoro with the first mate of the pirate king and Wss, would be worthless because the other members are acquiring the same types of haki without needing to be taught.
Unlike Luffy and Zoro, Kid and Law and the others are only increasing their scope of knowledge about types of haki now in Wano.
Making the others get FS and even Ryou at the same time as Luffy would make the training he did with Ryaleigh useless.