I continue to gather data.
Have a look at teams SR difference here:
https://docs.google.com/spreadsheets/d/1TBdpG3ahtD31QZ0Xn6HMygxruuIM1285n2cHCNHsNwg/edit?usp=sharing
The tendency clearly has changed from my previous comment about the issue. I am not playing at my usual SR right now, thanks to insane loss period. My hypothesis stands - matchmaker manipulates your win chance by shifting team SR. It actually pushes me up now - the games are MUCH easier and coordinated, than they were even 3 days ago. Explanation - team SR difference is in my favor almost constantly.