Yeah, poor leadership I would think, the Greeks held the better ground and they sought to engage front on...why not used the Legion's maneuverability and flexibility? They played right into the enemy's hands. The use of the Triarii was warranted IMO. The cavalry had to be stopped and the Triarii were the best at it. They should have been drawn up to prevent flanking in the first place, or perhaps use the Velites to harrass the flanking cavalry?