@Riot, Teambuilder Matchmaking (addressing again, I've seen this before)

I don't quite understand what's happening with the matchmaking with Teambuilder mode, especially when it comes to people who are trying new champions.

The reason I say this is because I personally was not trying a new champion, but somebody else on our team was (the Quinn), and the result was completely unbalanced (as seen in the screenshot below). Nobody is in the same division save me and our Fiddlesticks, and the rest are anywhere literally from Bronze V to Diamond II. Obviously, the game was boring at best for my team because we got carried by Lee Sin, and frustrating at worst for the other team that didn't have a chance for at winning. (Irrelevant, but I think possibly the Yasuo on their team was new as well as I played just as decently as he despite being several divisions lower. However, this could further have something to do with the matchmaking.)

So can somebody who actually knows explain how and why matchmaking on teambuilder works?