I agree the AI never seems to do well with carthage but it's a fun faction to play with. on veryhard/medium (i hate the fact that the computer gets valour bonuses i can't see and adjust for on harder difficulties) i played as carthage and controlled the entire italian pennisula by 245 bc. Attacking rome early is not a bad idea in this game, playing as carthage i knew they'd never leave me alone so i went on the early offensive took control of sicily, abandoned spain and then slowly picked the roman factions off one by one. . Italy basically became my breadbasket i'd extermanited all the populations of the cities and i was raking in the dosh. After that taking over the rest of the world was pretty simple.