If George Lucas had made that cutscene, the humans would have won. They had the high ground.
Sorry but I dont see what George Lucas have to do with this.
The humans didn't have the high ground, they were on a "flat" ground like the darskpwan were. Archers ofc, were high, but most of them were easily killed, and there weren't many of them anyway. I don't see why you question biowares decisions and making of this movie, and why you even care so much about it. It dosent even need to make sense, thou it does. Just considering the fact that the darkspwn outnumberd the humans BY FAR, (without considering half of those unist belonged to loghain), and don't forget that the darskpawn has units stronger then normal humans, ogers for example.