First the matchmaker looks at everybody's mmr.
Then it shotguns an entire flask of straight vodka and puts whoever wherever before it passes out. We're lucky we don't get eleven players in a game sometimes.
I am just about positive that the matchmaker puts your team together, then attempts to match it with a similar average mmr team that it has already created. This is, of course, absolutely wrong and awful, but it's the only way to explain how the two or three best players in the group of ten keep winding up on the same team. I jungle a bunch and I frequently get either games where I have three lanes with deaths before I get my second buff, or I can't gank because the enemy is never there when I show up.
And then you can throw duos in there, and the whole thing just starts spinning in circles.
Matchmaker needs to lay off the sauce, ranked needs a true solo queue, and wildly varying fourmans should be matched player for player instead of trying this averaging nonsense (two bronze and two diamond are not the same as four gold).
Time restraints need to go out the window. I would MUCH rather wait five minutes for a game with at least a thin veneer of fairness then get stuck with game after game of hilarious stomps.
Blind pick should just go in the garbage and team builder be the focus. You'd still have teams getting matched against teams but at least the mmr for each position would be (more) accurate. If it isn't already, it should attempt to find a team with a similar mmr for each position, too.
~Uiru