I assume do to the fact calvary used to be immensely over powered they are not substantially under powdered. They are almost useless in melee combat, horrible in a charge, and die on just about anything, against just about anything. They also have very poor morale from what I have seen.

Still they are useful for making half the ai chase you with 5 calvary units, but that is about it.

On occassion Horses do something that impresses me, but most of the time calvary is best brought to the battle in very small quantities. Like Artillery.