The main plot isn't as much about
(SPOILER)stopping the empire as it is about restoring Ashe to the throne, even though there is a lot of overlap between those two goals. I think the distinction is that the 'bad guys' are not that really antagonistic, but rather misguided, even though you could make the case that they are the ones on the right side. Rozarria is really only a bit player, and its leader, Al Cid, is played mostly for comic relief. You never get the sense that Dalmasca is caught in the middle of two empires, so that drains some of the tension out of the games final scenes.
The weird part about the last moments of FFXII is that they are set up as personal battles, even though the plot, up to that point, has more of a big picture emphasis. I understand why they had to give evil a face, but I would have liked to have seen them work on setting that up more throughout the plot.
There are a couple of scenes which hint at political behind the scenes stuff (
(SPOILER)such as the excellant scene where we find out Vayne has poised his father, and Gabranth is forced to kill Drace), but it never becomes the main focus of the storyline, in my opinion.