Since you are playing on VH battle difficulty, AI controlled stacks get +7 combat bonuses, which will make common strategies to deal with them a lot less effective. Do not be surprised if your elites can barely hold a line against levies.

Slingers are vital. They have AP (Armor Piercing) attacks unlike archers. This really helps with highly armored opponents.

You should also be aware that most Getai troops have AP attacks. As a consequence your highly armored phalanxes become tins in can, so to speak, if you are not carefully protecting them.