Why is it a problem? It is historically correct. The real world penalties were cost, training time and that they were slow, vulnerable to attack from behind
The catapult or trebuchet were much more expensive and hi-tech weapons
The downside of the ram was having to go up to the target, so it needed serious infantry support to survive very long.
The 0AD model of a few unmanned rams quickly flattening a fully manned fortress is so wrong. (or unsupported elephants same argument)
The catapult mainly damaged with fire
Why do cavalry have such high pierce armour? Foot soldiers, especially Roman, had large and effective shields. Nobody had cavalry with good anti-pierce armour until plate armoured knights in the Middle Ages
It seems to me that which is the best faction is a rock paper scissors choice and the map comes into it a lot too. The AI thrashes me on the high resource maps as it is simply better as gathering than a human. Very limited resources like Northern Island is much easier to win
Chariots were already obsolete tech at 0AD, they belong to a time when horses were too small to carry an armoured man and they had not invented stirrups