I feel you. My main account got fucked by recalibration and just out of curiosity I made a smurf just to see what I'd be calibrated at with a clean slate. The difference was 925 MMR a little less than recalibration dropped me on my main account.

Games felt better on my higher mmr smurf. Player quality went up, people played their roles, much less greifing and auto-tilt than my lower MMR main account. I stopped using my smurf and am trying to dig out of the trench.

The only explanation I can think of is that when we play too well consecutively matchmaking thinks were smurfs and throws us in with other smurfs and account buyers for a few games to even us out which leads to our loss streaks. It's so frustrating though getting like 3 wins in a row just to be slammed by "AFK END", PvE cores, and straight up people who give up halfway through the game and grief.