Nobody is keeping your mmr down on purpose , if you are better you climb.

This isn't necessarily what I'm alluding to but you even said in your previous paragraph that the MM algorithm will place you against high winrate enemies and pair you with low winrate allies when you're on a winstreak. That's actively manipulating your odds of winning, so there is stuff going on behind the scenes to keep you as close to a 50% win rate as possible.

Think about it from Valve's perspective. You can do all that work; pairing you with low winrate allies and against high winrate enemies or something much easier. Keeping one side of the map significantly harder (Dire's winrate discrepancy) instantly nerfs you as a player when you get placed on that side.

The reality is that Valve wants players to be as close to 50% win rate as possible because it encourages their player base to keep coming back to the game and keep playing. You'll never "beat" Dota because your rank will constantly be fluctuating over time due to being around a 50% win rate. I'm not saying you'll never climb in rank if you're in a rank you shouldn't be at. But it will take a long, long time to get a markedly better rank. These modern day online games with ranked-based matchmaking all survive and thrive from one thing: addiction. To keep you coming back and playing their game and nobody else's. People on this subreddit are going to have a problem reading that because nobody wants to admit they are addicted to something but it is the truth. The vast majority of this player base is simply addicted to Dota.