Let's talk about cavalry

[QuintusSertorius]

Whenever Ive used the Romans in a historically accurate way they always take much higher casualties than their eastern rivals, including any Greek faction.

Actually, I don't find this to be the case at all. Romans high frequency of armour, along with lots of units having high morale means losses are rarely that big. Facing almost anyone who isn't the Dacians or Iberians (lots of AP weapons...) in an equal fight I usually get 5-15% casualties, against 95-100% for them. Most of the kills occur during the rout anyway.