Another solution for a too strong Carthage is removing the AI cheat for province loyalty in case of revolts - Carthage has than a lot more do with keeping its heartland under control. They usually suceed (even if they temporarily seem to lose control totally and fractate, they are somehow able to make a comeback and become unified again), but it limits their ability to greatly expand outside. I like the dynamic it gives in game I don't play Rome or Carthage, since it seems to make historic outcome (Rome defeating Carthage) more likely. I'm aware that a part of this is the Roman AI profiting from the Anatgonist modifier (which is a cheat almost as big as the loyalty one) and it is a bit sad that its needed to get Rome on tracks, but the difference is here that getting Rome steamrolling is something the game needs for a historic feeling (while every blob being amonolith is not)