Welcome. That is a little strange. Usually stuff like that happens in bridge battles, but not on regular maps. However, the levy pikemen have "long_pikes" while the spartans hoplites have "spears." The long pikes are very deadly even if the unit itself is not so powerful. The pikes can kill before the spartans are in range to do the same. So if the AI foolishly charges, the long pikes can cause a lot of damage to it. The AI likes to charge pikes frontally. It also likes to suicide charge with its general. If he is mounted, the pikes will likely kill him in a second or two but the same could happen with a foot unit general.

Sounds like the AI was playing it very poorly (nothing new)...it should have been doing some real damage with the archers before hitting your lines. If the AI decision tree made sense it would force you to come to it by tearing you up with archers first (since it had them and you didn't.) Once it ran out of arrows it would advance if you had not. It could not have picked a worse strategy than it actually used.