I suspect this is a tough sell as CoW brings so much to the table, but try to ignore that for now.
Banshees - in legend, known for howling. Scary howling. REALLY scary howling.
In TT banshees howl and paralyse, creating an exciting glass hammer unit.
In DoW, banshee howl is probably third fiddle when compared to their other talents. I personally think it has the best SFX in the whole game and I love it, but it doesn't seem to do a lot. As mentioned, CoW brings morale rapage with it, but I'd feel more satisfied if it came from the special ability than an inherent ability.