Rivendell Revelers can't seem to use their Akallabeth power on the main gate, the main tunnel in the chamber just before the throneroom, or the throne. The power appears to be activated, so it goes into cooldown mode, but there's no effect or damage done.
Rivendell battering rams do no damage to aforementioned tunnel or throne. You can attack the tunnel, but it does nothing; but it won't even attack the throne. Units also cannot attack the throne.
Misty Mountain AI, as Soldier level AI, do virtually nothing after building structures all throughout the fortress itself. Only a handful of units are used to defend it.