Nah all the comp has to do is make good calculations. Like the city of Antioch, it will never get sacked if you have a reenforcement army that can reach the river crossing to the south in 1 turn, All I was doing there was waiting for mercanaries and reenforcements so I could actually take on the comp in a fair battle but the comp comes after me and get's mutilated. Also the comp needs at least needs 1 campaigning army. 1 that does'nt turn back untik it has taken a city or defeated a large army but only if it is depleted. And when the comps laying siege to look if an army is a threat, 1 town watch can pull an army off a siege. Now I do'nt exploit this but sometimes you are moving troops around and the comp gets distracted and makes a worthless move on a few hastati or something else.

Of course the comp could gather a 20 unit army in hiding and then go on raiding parties and sack cities, then leave and have a diplomat give the city back so there is'nt a rebellion in your favour.

Also when the comp assaults a city it needs to be able to exploit multiple breaches instead of trying to bumrush 1 gap.