As others have implied, life is not fair.

The game is, probably, more balanced than real life. Version 1.0 cavalry rules would leave the Romans hurting if the AI was even halfway as good as most of us would like to see.

Historically, the answer to Rome's strength centers on a number of issues:

Discipline -- few if any of her opponents had the military discipline Rome instilled. Undisciplined troops are wheat before the scythe of a disciplined force.

Insitutional Strength -- when a good King died, his empire often went with him. Rome's oligarchical republican institutions, even adulterated by the Empire, gave it profound strength

Persistence -- Romans never gave up. It took Marius years to break the Numidians and years more just to build the road to get to the Cimbri properly --- so he did. Hannibal wandered Italy for decades, so they waited him out and sent a decisive strike force after his home base.

Engineering -- Roads, aqueducts, nightly fortifications, and superior siegeworks. Romans did more to further their empire with picks and shovels than with their gladii. Infrastructure begets economy, economy begets increased tools for warfare and money to fight. The brave warriors of Gaul were, to some extent, beaten by the Vie Appia et Salaria et Brutia, because commerce flowed along those roads and supported the power of Rome.

SF