Well, yes they do have quite some good archers that certainly have some impact on the battles, but I don't think thats why you guys lose alot of battles.
I fought for both the UIF and the Northern Alliance and the UIF is just far more organized. If only half of the people listens to the commands of the commander and the other half just charges in like some braindead squirrel then of course you are going to lose battles.
For example, this battle -
http://c-rpg.net/?page=strategusbattlesarchive#!?page=strategusinfobattleroster&id=1009You guys had better gear, more people in the rosters and yet you guys lost really hard and even retreated when there were like 900 troops left. What even happened?
If I could I would've signed for the underdog in the castle battle today but im banned (again) for 2 weeks