I'd like you to really think about this. Why is the matchmaking for ranked matches based on MMR and not just our visible rank? MMR has been in the game since ranked was introduced way back in season 1. However, at that time there were no leagues or divisions to climb through, just your MMR. Everyone started at 1200 and you gained and lost MMR as you won and lost matches. This was fine and the matchmaking meant that you were grouped with people of a similar MMR.
Now though we have effectively 2 ranking systems (MMR and leagues/divisions) that are constantly conflicting with one another. This used to be ok because when the ranked leagues and divisions were implemented you couldn't drop down a league. So for example if you were Gold you couldn't drop down to Silver, no matter how many matches you lost, but you would still lose MMR rating. This kept the matchmaking relatively balanced, but that isn't the case anymore. Now-a-days you can drop down leagues very quickly if you lose too many matches, so why do we still have MMR?