The main point from what I want to say is people are using champs that they don't even know how to use in rank. Some players are trying new champs (or showing some cool new skins) in rank game instead of AI or normal, which makes them play worse and cause their team lost. So I am giving a suggestion that mastery 3 or above is needed for rank game, no matter if the player knows how to play or build the champ or not. At least it will kick out PART of unskilled players in rank game, not all, but part of.
Some might play good at new champs. Maybe they tried it in PBE or they are born to be good at it, but it is just a small group of people. Just win around 4 or 5 games in normal then they could get mastery 3 champ and enter the rank with it. Again, mastery 3 is just a suggestion for Riot and maybe they could have a better solution for this.
I don't know how you guys treat the rank game mode. Is it just another mode similar to normal? Or is it the mode for players who are trying hard?