Strictly speaking on the MMR front, everything Blizzard ever said about Competitive and its matchmaking has been compiled into this topic:
It’s a very extensive References section on the bottom of the post.
As for general match quality, the entire balance of the game, first and foremost, is made around fully-organized teams taking on other fully-organized teams. This was never exactly meant for random matching randoms with other randoms to take on other randoms. You could argue that this kind of game was too idealistic in nature to be feasible, but I’m pretty sure that in primary schooling all over the world, people at some point had no choice but to work with other people even if they didn’t want to.
That being said, the actual rank very much factors in for so many players (just look a couple posts above you to see someone complaining about the matchmaker intentionally giving him bad teammates).