So since so many factors look to be depending on the leadership abilities of the general involved, I think we might have accidentally stumbled across a balanced Vs. match. I know, everyone take a minute to sit down while you recover from the shock.
I'm still a bit skeptical on the 'looted Terran units' thing, though...Tarsonis had been occupied by the Zerg for a long time, and they pretty much trashed everything capable of fighting back when they took it in the first place. I honestly can't see the Orks finding enough equipment in salvageable condition to actually field an appreciable number of Looted Valkyries or Looted Siege Tanks; they'd be much more likely to get field-stripped and rebuilt into Battlewagons or Fighta-Bommas.