Tried again. Benchmark was the only survivor on 3 HP, used Setting Sun Ra's incap ability to take out Plague Rat for the win. Predictably, no unlock.
What the heck is this mystery factor? I'm checking the logs again...
EDIT: Okay, I checked the two prereq logs here, and I noticed something that I think may be the key to it. It could be a coincidence, but it stood out a bit, so it could be important.
At no point in either game did Benchmark defeat a villain by using a power. The environment was 'allowed' to take out a villain, but whenever Benchmark took out a villain character card, it was with Fly-By, a Hardware effect (Onboard Cooling Tubes and Secondary Cannon), or Countermeasures.
I'm going to test this when I get the opportunity, but right now, my hypothesis for the unlock condition is, "Win a team villain game against Baron Blade, Ambuscade, Fright Train, Friction and Plague Rat, using a team including Benchmark, Fugue State Parse, and Setback. Fugue State Parse and Setback must be incapacitated, and Benchmark must not defeat a villain using damage from a Software card. Then, Benchmark must play a Hardware card in a game against standard Baron Blade."
This needs refinement, because, duh, but for now, that's my thinking. Feel free to tell me if your unlocks ruin this idea.