Welcome to the forums Slash

I've had similar experiences with AI control in the past. The only issue is what you do if you need the extra troops. If you have a twenty unit force and there are re-enforcements available, then you either go for a gradual drip feed of troops which will be well managed or have them all come on to assist at once under low quality leadership. It's often a very difficult balancing act, considering the size of the enemy and the chances of victory in each scenario.