10 game minimum exp on a champion before ranked?

So i am in silver 3 (new account) and i notice people first time a champion a lot in ranked. I watched my friend First time lee sin and I face palmed. He totally lost his team the game. Theres games where i carry and i look up accounts of feeding players and sure enough. Last 5 games 5 differant champions, all losses. So why is not playing 1-3 champions only not more encouraged (in ranked) There should be a 10 game minimum in my opinion. I know people have the urge to jump into ranked after one lucky normal game. But take time to learn the champ.. if you go up against any mains they will destroy you hands down. ( if in same elo)