The Double Standard
If you work at Riot and you're experienced with a champion, you're allowed to affect balance of that champion, it's literally handed to you because you're the one who knows better.
If you're a player with experience with a champion, you just have "player perception" of that champion's balance, may affect some things but may also (likely) be completely ignored (Cassiopeia, Mordekaiser, etc.)
I hope I'm not the only one who finds this "player perception" terminology incredibly insulting. I don't think Rioters have much opportunity to play the game more than notable streamers and champion mains in the community, so it's not like they really have equal experience or authority on a champion. And telling people with 1,000's of games on one champion "That's just your perception" when they try to give feedback is straight bullshit.