Seriously, the only people who would look at that cutscene and assume it couldn't have been the site of a battlefield are you guys, extreme fans and well versed canon people. People who are unfamiliar to the Freespace universe would have come to the conclusion that all those Marines died in combat somehow. And that's the point. That cutscene is so contradictory to canon precisely because the creators don't care about canon. The intended audience is not to attract people who are familiar to the FS universe, but to attract people who are not. It's intended to simultaneously visually demonstrate how devastating the Great War was in terms of human lives, and the terrible power of the Shivans to those who are unfamiliar. Just showing hulking space debris would not convey that image.
Does that mean ground combat actually did occur? No. The problem you guys are having is that you're trying to fit the cutscene around your concept of canon.
Now, I dare anyone to prove this next statement wrong: the people who made the cutscene did not give a sh*t about the official canon, and Volition rolled with it because they also don't really care about their own canon, when it comes right down to it.
Don't try to fit things like that cutscene around canon, it's fruitless and pointless. You can't try anyway. Why would one image, the marines for example, conform to canon when the crashed Hades clearly doesn't. Why would any of that entire cutscene conform to canon at all? It doesn't. Acknowledge its purpose, which is not to add anything to canon, or even to conform to canon, but to visually convey a concept.