(Sorry!) One thing I remember noticing when I was modding the map way back when, was that most factions only expanded in one general direction when the game first begins. The Julii expand into Gaul, Scipii into Sicily then Africa, and Brutii will go Greece and conquer northward.
Carthage is different from all of those people though. They have so many different ways to attack, and are so spread out, that when they do finally commit to a front, they are too weak to face the concentrated foe that awaits them. When I gave North Africa a few more regions, and made the Sahara unconquerable, as well as making Sicily either Rebel or Carthaginian possessions, Carthage would generally focus on conquering all of North Africa, then focus on either Sicily or Iberia. When I talk about them focusing, I mean there would be multiple stacks moving to the same front.
One curious thing I noticed about making the Sahara unconquerable, was that no one would march through it to get somewhere. The AI conquers provinces that border it, and if it can't conquer it, it will skip it. If the only way to get to another province is through that unconquerable province, it won't even consider going through it. This made it easy to separate Egypt and Carthage from butting heads.
So tl:dr, AI Carthage needs a better map and better barracks/units early game to succeed. Anything else would give them a boost but won't solve the problem.
I am the Carthaginian who became an angel, and surrendered his wings for a life on the sea of battle.
My magic screen is constantly bombarded with nubile young things eager to please these old eyes. This truly is a wonderful period in which to exist! - Terikel the Deflowerer