Bononia is always hard because of the elite Gestatae naked warriors - better than anything early Rome has, man for man. Gallic cavalry is also better than Roman.

The average Roman unit is better than the average Gallic unit, but the BEST Gallic units are better than the best Roman units.

Rome's greatest strength is not her ability to win every single battle - she doesn't. Her greatest strength is her ability to just never accept defeat, and win every single WAR as a result. When defeated, Rome just builds and sends another army. And, if necessary, a third and a fourth! Victory at any cost!