I agree with moto on this. Even on hard AI the AI still makes some totally irrational decisions.
Charging a trench filled with machine gunners with only one or two units of rifleman. dropping bombs on an advancing wave of troops instead of dropping in front of the wave (were the wave will be by the time the drops start hitting). basic stuff like that. Oh and I dont think the Ai handles the game differently depending on the unit settings. for example i've turned off tanks and support and it still spreads its units out instead of building up forces.