yes but the romans knew the value of cavalry and they used it very efficiently
No, they didn't... Their armies were almost entirely made of heavy infantry, legionaries and mercenary auxiliaries.
Only a very small part of their army was some cavalry and archers for some support. How do you think, why they couldn't beat the Parthians?
Also, what Rome we are talking about? Republic of Rome, or Roman Empire?
Because in Republic of Rome cavalry was very limited, but in Roman Empire, eastern(Greek) part cavalry was a pretty valuable force in fight with Sarranids and(later) Arabs.
If we are talking about game based on Roman Empire then game would be boring as hell.
Two very strong factions and few others, way weaker.
Also, even if we'd talk about Roman Republic period, then formations would be absolutely necessary
for this game to have any sense.
No fan of ancient times would accept Greeks and Macedonians fighting without their phalanx formations.
Also, naval warfare would be extraordinary important too.