I think it depended on the situation whether it is more difficault to attack or the defend. Take a look at massda or alesia. The romans outnumbered their enemies but still werent able to storm the cities(fortresses). And i mean the romans had formidable siege equipment and with the legioners quite heavy infantry. The jews and the gauls had the geographical advantage. The fortresses were built on hills, which made the siege equipment more or less useless.
The battle of hastings is also a nice example, although it took place 1000 years later, the equipment didnt change that much. The saxons had also the geographical advantage, but were fools enough to give it up.
I would say you cant expect a game, with lets say "rules of playing", to show you it could have been in the real past.