You should NOT be allowed to play champs you don't know how to play in ranked.
Recently I've lost a few games where my teammate was playing god awful, and an enemy was trash talking them then my teammate responds with 'hey its my first game as XChampion"
I lost my mind. I literally stepped away from my desk for a second, we are losing because some goober wants to play ranked with a champ they don't even have any idea of how to play instead of just trying them in normals first.
It's so BS and seems like common sense that you should have to play a few games with a champ in normal before you play them in ranked
Even if its just 5 normal games, or hell even 3 that would be SO much better, 3 games isn't unreasonable, yeah it would be a bit annoying but a minor inconvenience for one player saves 4 other players from a lost game.