See I think this would be a good idea to really enhance the ranked gameplay experience
http://wwg.com/2017/02/06/league-of-legends-tip-of-the-day-ranked-isnt-for-practice/
You should be comfortable with a champion and know all their tricks. Like that graves player said, he didn't even read his passive. I know people that main champions and do not know their abilities simply because they never read them. Seems like an awful excuse but it's reality.
Having a mastery level 6 requirement would be an awesome change, it shows you are dedicated to this champion, you know how to play and play them well. Imagine if you had to work to get 20 champs up to , 6 before you play. There would be much fewer trolls able to hop in and ruin your day. It would be a more competitive environment because everyone knows everyone is good with their champion. Silly mistakes will be capitalized on and punished from experienced hands.
Sure the first time zyra support might land some nice combos but chances are she's going to miss that snare again and again
Im in silver , I can attest that there are first timers in games. You just lose hope in lobby and buckle in for the next 40 minutes, for this person will be dying over and over. Norms are for practicing your champ and honing your skills when it seems people will watch LCS and try a new tactic in lane immediately after watching someone else kick ass.
I really think it's a fundamental flaw in the league community though, there are so many trolls, and this game managed to boost and BM all sorts of people with ease. Many many players think they are way better than they are. The majority of players are sitting with me, in silver, just being casual. And that's ok. But for some (riven players) they just have to be the best player in the game.
I've played casually since s1, accumulating over 2000 games of league. Many people have more. I've wasted so so so so much time because of other people implementing their own rules and agenda on this game.
If you want ranked to be an authentic representation of skilled players matched up for an intense, action packed game, having a requirement like this would weed out the trolls and ensure only the most dedicated players are willing to lay down their LP and try to make it to the top. I know this probably won't be read by anyone important but that's my 2 cents on the issue!