What am I doing wrong?

[krpeters]

No, I gave it a try. Without the etherealness, a bane lord gets hit too often by a horde of Dai Bakemonos, routs, and dies. With the etherealness he gets chewed up and spat out due to insufficient protection (even with boots of stone) Meanwhile, the ethereal gargoyle or an ethereal ironskinned troll king pound on them relentlessly. Admittedly the extra HP of the gargoyle and the regen of the troll king help a lot.

Like you point out, anything with a magical attack is going to be a problem, but I'm trying to kill chaff mostly.