Funny you should mention that. I went on and played a custom (10,000 denarii scale) battle against the germans in the Prippet Marshes (?). I took the advice of previous posts and dumped the onager and velites and picked up 2 more aux archers and 1 wardog and 1 more peasant. So now the army looked like this:
2 gen
2 praetorian hvy cav
1 leg cohort w/eagle
2 leg cohort
1 hastati
2 auxilia (spearman)
3 aux archers
1 wardog
2 peasants

Germans fielded usual 3-4 cav mix (gen/noble), spearman, axemen, swordsman(?) more bezerkers, warbands, archers (the "good" ones) BUT no women this time. Must of left them at home.

The deployment was a little different since the bulk of the right side area is trees with sparse trees and fields for most of the left side. I deployed foward (un-usual for me) with a group of peasants way far left in the open, one cav wing (gen/hvy cav combo) archers and war dogs in the patch of trees in the center, peasants in the open between center and right trees then the bulk of the force in the right forrest area with the archers positioned closest to the field along with my right wing cav, infantry supporting behind but to the right to "wheel" through the trees as the germans move by. AI is definately a computer because when it saw the peasants it sent half of its cav to my far left after them. It then committed cav and forces to the peasants in the center/right after I advanced them foward then ran them back (bait). I kept the archers from opening up right away (which is a pain to control), started swinging my hvy inf in a wheel motion, hastati and aux to support my now detected archers etc, and committed my cav wings in an attack from 2 directions. By now the AI is splitting spearman attention in different directions (due to war dogs running out of the center woods into his warband units) and movement of troops in the woods. BOTH my gen and the german gen ran away from this fight (?). Now its nip and tuck, toe to toe with his earlier cav adding to the fray. In the end, I wipe the germans out for the most part but once again I lose half my men. One thing I did notice by accident and don't know if this will work on a larger scale, but if I used my auxilia (spearman) head-on against his phalanx spearman I could at least hold them long enough to wheel a cohort around the flank, once they break the Hastati are fast and between them and what was left of my cav I could run them down. Anybody know how long auxilia can "hold" these guys? It could be a useful pinning stategy, but for how long I don't know. Both sides in this case were pretty whittled down when I started doing it. Is it common just due to "battle" to lose half your men in a victory, thus the price of war??? It could be painful and costly in a campaign game, especially if your losing "seasoned" troops.