PSR was much easier to farm earlier in the beta, back when a lot of the features were being tested or hadn't really been implemented. The best players, along with some not-so-good but extremely patient players, hit 2k+ psr fairly quickly - one game against a group of 5 1500 players with just you on the other side, and having all 5 of them leave, gave you a shitton of psr.

Also, elasticity made a big difference - I got to 1870 psr by riding an extremely good arranged team, with a strong combination of heroes. Then, the next day elo elasticity was put in (you know, after you play a lot of games, your psr gain/loss stops varying so much: the theory was that the more games you play, the closer you get to your true psr). Thus, when I lost about 17 games out of 20 over the next few days in my psr range, I only went down to 1810 or so psr, though my KDR took a much steeper plunge.