All the claims about the AI problems seem to be pretty much accurate. Me and my friend played 4 custom multiplayer battles, two land, a naval and port assault. In every single one of them the AI pulled some pretty herp-derp moves.
Worst one was during the port assault and we defended. We agreed just to do land troops and have them attack us in the city. I accidentally picked two ships in my line-up, so I decided to just park them near the city for backup.
We took out their tiny attacking force with 6 million siege towers ( give or take ) and then their 20+ ships just sat outside the town, after 15 minutes we tried to walk up to 'em and fire some flaming arrows etc. where we sunk a ship or two ... Still nothing.
Then my friend mentioned the ships, they probably won't attack with my ships on the ocean. So I ran them up there, they killed one or two of his, they got blasted and BOOM! His landing started. So the AI will just sit around until you zerg your ships, because they won't chase them.
Stupid.