It seems to me that the baseline is 3000, but it doesn't make any sense if I get 3850 rating after like 6 lost games and two games where I fed on purpose to annoy Russians, and then someone else gets like 3400 after more won games. Volvo's formula for this must be really epic, again.
The way I see it, a MMR that really meant something would be really, really hard to make but possible. You'd have to have an extensive database of all heroes and their roles, what kind of GPM people have on average when losing/winning, game duration, assists/kills etc etc. I'm 100% sure that Volvo didn't spend enough time on it to get a sophisticated MMR system.