Chaosmancer
Legend
If you say no and the player says yes, what happens?
We discuss the rules like adults.
Again, seriously, this insistence that it is utterly impossible for the game to work unless someone is the unquestioned authority is getting old. You aren't proving the point you think you are proving. Yes, maybe it is possible that after a discussion of the rules, reading over the text together and a discussion of play priorities and their expectations two people will have different opinions.
What happens if we two agree about their character, but some third person who isn't playing the character disagrees? What if three other people agree with that guy? What if Treantmonk posts a video essay on why we are all wrong because we missed this rule? What if DnD Shorts says that video is wrong because he didn't read an errata?