players trying NEWLY bought champs in RANKED

Recently i have encountered players who play Ranked matches with champions they bought recently...i play solo ranked often and few days back there was a guy in our team who played zilean and it was his second time playing with that champ and because of him our adc couldn't play well and we lost that match because of him and there was one more time a guy who came with illaoi in ranked. Its already difficult to climb the bronze ranking leagues because of lot of beginner level players joining in ranked so RIOT please do something about this. Thats why You can change ranked games by making a rule that only champions who have mastery level above 5 should be eligible in ranked that way players cant come with newly bought champs n ruin the game for others.