Well if you think about it you are advanicing into a wall of 10 foot spears that you can't flank, it's not meant to be easy. I did an experiment, I made an enormous Roman legionry army (10x urban cohorts, 10x First Legionary Cohorts), then I gave myself two units of Spartans (if I only had one it would be minced by the Legion's pila) and 4 units of archers, everyone (on both sides) was max promoted, needless to say I won.