Egyptian chariots are tough to face because they have high mass, multiple hit points, a dangerous scythe attack, and they are fast, using a horse model that has the fast horse skeleton rather than the standard horse. This allows them to zip in and out causing havoc to your forces with ranged weapons, or smashing into vulnerable points. Historically, chariots were not quite so mobile as cavalry and had real trouble with anything other than smooth ground. (About the only real praise you will hear of them in the time period is Caesar praising the way the British celts used their light chariots.) Mass determines the penetrating quality in the game.

If you can ever bog them down they die quickly, and the are quite good at killing their own when under archer fire inside a city during a siege...I've seen them mow down many hundreds of their own before with the scythes, leaving only a few chariots and men for my forces to mop up.