The factions can be strategically balanced AND historically accurate. The Romans had a very hard time building their empire. They didn't simply march around and accept surrenders. Varro, Crassus, and Varus would all disagree with the notion that the world was theirs for the taking. Even winners like Scipio and Caesar would admit that outcomes were often close run things.

The fact is we have no reason to believe as yet that it will be easier to win with the Roman factions than with any other.