Matchmaking??? (not a rant)
From my experience it should match up with the higher end of your party’s MMR, at least that’s what happened to me, came back to the game after an eight month break, so, not so great MMR, played with a friend that regularly pvps and instantly got matched with ESL guys.
It can happen two things as far as I know:
You either get matched against a team equal to yours, from rank 10 to rank 80, so there is unexperienced and experienced players,
or
you get matched with a team with the same average team MMR as yours, but everyone is medium experienced players, that is, not as experienced as the rank 80 in your team, but more experienced than your rabbit rank.
This may cause some imbalances in the second case because the low ranks will feel useless versus some more experienced players.
Again, this is how I think matchamking works right now. I might be wrong.