I believe that MMR should be taken away completely, and just have leagues in its place
Instead of having MMR, why not just have leagues as your true ranking?
In the current system, if you are Gold 3 with a higher than normal MMR, you get matched with Plat 5s/Gold 1s, however, if I'm at Gold 3, and I get matched with people where I belong, how will I move from my ranking at Gold 3?
If you just have Leagues as your true ranking, and MMR is no longer there, say you are Gold 3, you will only get matched with people 1 tier above you, and 1 tier below you, aka Gold 2/Gold4, which would be a much more true representation of you being better than the league that you are in.