I see large armies being left in useless positions while factions are getting hammered elsewhere all the time.

I have even seen the greeks with a full stack left standing near Sparta while it was under siege by the Brutii with a half stack. I don't know if the ai thought that they couldn't win the battle and so never tried or what.

If the AI sees that it can't win a battle with the closest stack does it not even try to fight? Then if there is no better army to bring along they resign themselves to losing? Seems like the stupid ai works this way.