Militia cavalry as noted above are the savers for the greeks, learn how to use them fast. They operate best in pairs, and require a lot of micromanaging, but with them working together, they can take out a legionary cohort with hardly any losses.

The AI tends to get disrupted a lot by feints from then, use this to draw units into a two on one situation, then try and hit them in both flanks simultaneously. Against post marius romans, often the legionaries will try and go testudo after a few volleys. Hit them just as they begin to flick their shields up with both units and it will crumble.