You are facing a classical catch-22 situation, now your initial problem is that since the 1.1 patch and probably even before that CA has implemented the following fact:

All the player's artillery pieces are chosen in the initial 16.. This implies what holds true for you will also hold true for the AI.

Your second problem is that in column 11, the probability of artillery showing up as rebels is too high, which is why you get singular events such as 12 ballistae and 4 Hashishin rebellion that someone reported a few days ago.This can be easily be modded by repplacing the factors for artillery with some other unit like Almughavars that appear very rarely in the game.

Now we come up to the Column 15- Now here you have to mantain absolute certainity about what you want, for if this is set too low you will end up with the AI rarely developing artillery and getting slaughtered when assaulting castles, set too high and you will end up with a magnified version of your orignal problem.