And, as far as adding in a fight scene, we might be running upside budgeting concerns. Adding in the money for what would be an actually fairly pointless fight - since we're all agreeing that 7 of 9 isn't going to end with a fully functioning Cube complete with Borg army - this is the cheaper way to go.
It also plays very strongly into the narrative that the Borg are victims. They didn't get to fight back at all. They were just killed without a second thought. It does serve to "humanize" them to some degree. If they were fighting back, then the Romans would have some justification for killing them. But just flat out gas chambering the Borg drones is pretty hard to justify.