For purposes of tests, Brutal functioned similar to Hard
Edoras:
Medium AI, functions properly, no issues. Sieges Edoras.
Hard AI, stayed at their camp, did not leave camp unless attacked directly, would not defend allies.
Minas Tirith:
Medium AI sieges properly, top AI has issues thanks to walls being close to their base.
Hard AI did not siege, top AI has more issues thanks to walls being close to base. Opening gate would entice attackers
Helms Deep:
Both AI has issues. Neither sieges. Opening gate would entice attackers
Pelargir:
Medium AI sieges, functions properly.
Hard AI does not siege fully. Sends occasional archer unit to fight trebuchets. Opening gate would entice attackers
Top right AI has issues due to small area and closeness to trebuchets, particularly the big trebuchets.
Dol Amroth:
Middle AI has issues due to small area. Evil AI able to function, Gondor was not.
Medium AI was sieging from sides. Middle depended on faction.
Hard AI did not siege. Opening gate would entice attackers
Caras Galadron:
Tried to play. Weird fortress mapping with hill causing map view difficulties. Goblins were the only units actively sieging during limited testing.