Matchmaking, Ranked, Team Builder
Let me go on record and state the following: Just because you're a Challenger Mid Laner Assassin, doesn't mean you're a Challenger level support, jungler, tank, adc, etc...
That said, perhaps the Ranked thing should have this annotated, different ranks due to different spots you take. You Mid assassins and you're a Plat. Great. You go bot lane as ADC but have never really did that since you started playing the game, you clearly not Plat in that position. If there was a way to show the rank according to position, or a way to have ranks per position, it would probably help a little bit.
Onto 'Match Making'... I understand some folks want practice, but it's odd for folks to run in and have say, lower summoners fighting 30 golds and such, and if the 30 golds get destroyed, everyone mocks them. It goes back to champ familiarity and lane experience (I would guess). Plus, when you get someone who is high ranked and in their 'comfort' lane taking on, say, a s.lvl 10 in same lane, one of them is going to get smacked around like a noob, all day, every day. They won't know if they were getting better or if they were getting worse because of the skill gap difference. But that's something harder to keep up with I'm pretty sure. You can't just penalize 'ranked' folks for match making... well, unless more specific rankings were made to move them out of 'bounds' for that. "Cannot Lane with S Mastery Katarina, Mr. Challenger Level Mid Laner. Please choose one of lower mastery."
Though I'm sure folks would get upset about that. (Some folks play just to have the 'Rambo' syndrome.)
I know ranked has the 'banned' thing and that's all fine, but maybe a Team Builder Ranked version could be implemented to help coincide with the champion mastery thing that's being evaluated. This would have, say, Top Lane Garen who's gold go to master another top laner or two so he can go into the 'normal Ranked' games and gun for top lane, JUST in case Garen gets banned (Like that EVER happens but... examples).
Any comments to help make things more acute and accurate are more than welcome. It's just one of those things to help lower skilled folks battle closer skill level so they can learn as opposed to getting 2 shot in lane due to inexperience. And... Ranked not just throwing rank around, even if they have NEVER done that role or lane before: "I'm Mid Lane, Diamond Level Akali, I know all about Jungling (unranked) and you're doing it wrong!"