The original money script did give them a set amount per settlement. It caused them to recruit low-level troops in all their cities and never build any buildings. I had a fight with 3 gaesatae units against 28 lugoae and won (although my guys were about ready to call it a day many times during the fight). Yes, that was all they produced. The script I made for them now makes sure they have the opportunity to get loads of money every four seasons, if the dice are in their favour. This means they will upgrade and get better unit mix, but not spam too many troops so that it's impossible for the AI to expand.