[Ironhawk]

I have had plenty of success, yeah. The key to beating the AI is two things:

1) Manipulate your empires "stats"
The AI can only understand your empire via generalized numbers. Most important is the Army Size - the AI doesnt know that you have 400 dual-blessed helhirdlings, only that you have 400 units. So, buff up your army size with cheap garbage troops (like militia) to stay in the #2 or #3 position on the chart. This will make the AI more likely to attack each other, rather than you.

2) Employ army-killer strategies
The AI pretty much only uses enormous hordes of troops with no strategy. So, all you need to do to counter them is employ the tactics that are more profitable against large armies. The easiest of all of these to implement for you is probably Artillery Spells (Murdering Winter, Fire from Above, Beckoning). One cast of these spells can kill up to 40% of an army of human troops. The next step would be army-killer spells like FireStorm, Wrathful Skies, etc. If you prepare your mage properly, he can defeat entire armies with these. The most complicated route (but perhaps the most effective) is to summon and equip powerful SCs who can kill basically unlimited numbers of mortal troops.