You are right, the AI really is not equipped to deal with walls. That's why I don't use them versus the Computer players.
An interesting thing, though, is that they will push very hard (and send all they have) to kill your farming and fishing operations.
The CP will send guys to your TC and scout ships to your docks early in Tool (being that "early" is not that early, even in hard).
When you play against 3 CP, you will win most of the time, with the conventional fast Bronze approach. The CP also handles Ctapaults and Priests much more expertly than humans (have you seen a computer-controlled Sumerian cat rolling and firing smoothly without stopping?...).
I have save a few "unsolvable" starts, and so far been unable to win most of them! This happens when 2 of them succeeed to make the trick of using a staged attack (1 tool "rushes" you, the other will harass you in Bronze and the unmolested one will pound you with Iron stuff). You will notice that the computer also uses hoplites very effectivelly, combining the hoplite attack with a cavalry one, which is very effective.
Weak points of the computer that I NEVER explore:
Never attack a building and then kill all his peons that come to repair the building, one by one.
never build walls that it cannot handle.
Never use more than 50 population limit (the CP's AI just cannot handle more than 50). In fact, I make a point of that, because it really is more stimulating to fight 150 or 200 units with your total of 50-65 (with over-building) than to just massacre them.
Sometimes, the Zone is terribly busy or unstable and I can't get a good game, or I'm on travel and can't connect. This is an occasional time to try this mild form of fun.
Sometimes also, the CPs will beat you - good, it gives you some reason not to discard it altogether...
But, as a rule, human opponents are a much better game.