Just rewrite the whole AI. Seriously.
In harder modes they shouldn't be cheating, they should be smarter.
"Harder" shouldn't mean that your AI team suddenly becomes dumb and sometimes just stands there doing nothing, it should mean that the opponent becomes better.
Also, the AI should "play the game".
If it's a flag holding game, it should play to hold the flags. If it's a killing game, it should play to kill. Instead the AI ALWAYS tries to go for the citadel. During fortress destroying games, given the choice, the AI chooses to go to the citadel instead of destroying a fortress that's RIGHT THERE IN FRONT OF IT.
That is not the way to write an AI.
Yeah, "it's not that easy", some of you will say. They manage to do it in other games, don't they?