in rome total war when your city was under assault, all u had to do was set up a really good defence in the center of the city, and let the towers on your walls do all the killing. i hope in M2TW u have to defence your walls or else the enemy would start sacking your biuldings and killing your ppl, so theres accual consiquences to not defending your walls. it would be a whole lot more realistic, also if your troops could, go in biuldings in a city, killing the ppl inside. Then even if they didnt take the city at least some buildings, and hav killed some civilions.