There is so much wrong with team game matches. As result the ratings will never settle down before the devs will fix the issues.
The previous calculation was terrible and the new one is pretty exploitable by smurfing, so smurfing is becoming an issue (the 1200 players are probably much better, but play on a second account, that is the issue which you descibes). And then we also have the dodging issue (The Alt+F4 Multiplayer Problem)
Solutions for this issue are already posted in multiple threads. I dont feel the need to repost them in this thread as well.
Previous system was terrible. Ratings were inflated and therefore meaningless. They most likely say more about the play rate then about skill. Therefore they made a change, but smurfing was a oversight of the devs in the new system.