is the AI cheating

[thejeff]

PD 50 cost 1250 gold, PD 75 cost 2850.
If it can stop 100-150 troops, since he's worried about 400 to 500 it'll often just get destroyed. Or it'll sit in the backfield and never get used.
Use PD to stop the nuisance attacks. You need real forces to deal with the main armies.

As for supply, even new he can deal with supply issues better than the AI can. Boosting supply is a standard way of boosting the AI. It might help him, but it'll help the AI more.