Besides, Roman cavalry was of really poor quality. In their Greek battles they relied more on their Greek allies (yes, they defeated the Greeks with the aid of ...other Greeks) rather than their own cavalry.
Thats interesting, at the moment Greek cavalry is the worst in the game (no heavy cav other than General's Guards, and Equites beat vanilla Greek cav and Militia Cav).

Looks like the Pre-Marian Cav needs to be Nerfed.