Players need to be prevented from trying new champions in ranked

There's no reason I should be losing 20 LP because I have a 1-9-3 Ezreal on my team who thinks he can't E out of Veigar's stun, and picked him 'because he looked op.'

This is something that can be caught and prevented in the lobby. I don't care if we have to play three normals with our entire champion pool in the pre-season if we want to continue with ranked, but something needs to be done to fix this.