What's the point of having MMR in ranged and your rank? Without the MMR we'd have a more reliable ranking system where your rank determines how skilled you are. MMR just muddles it, putting in a secret extra thing for Matchmaking to mess with.
So MMR tries to match you up with people around your skill level, but of course that doesn't work right, we have all been matched with people much better and much worse than any of us anyway. And sometimes you get matched with people way out of your rank.
Maybe rank matchmaking should just try and get you with people within 1 rank up or down of you so you are always around people of the same rank to compare yourself to.