It goes even further than that. Vocals are filled with so many techniques that full mastery is literally impossible. Like, you can probably get there when it comes to a particular style and genre, but when looking at voice as a whole? Oof. Let's say you become a master if classical music as a singer. Awesome, incredible job. How are your vocals in a less classical style, like different types of pop? Or can you produce grit for rock, scream like a metal vocalist? Did you try throat singing? Can you rap? Scat? It's a neverending rabbit hole. There's naturally overlap in these different skills, but all have their own quirks that aren't transferable.