The banshee wail comes into play so rarely and even more rarely does it cause death (I think i had 2 with my last 250 hour necro that had it). On the flipside the non special undead (ghoul) holds you in place for 5 rounds, very few people survive that hold and it fires much more frequently than banshee wail.

Honestly the greater undead are nifty but in terms of raw killing very few of them are even situationaly better than using a ghoul. It would be cool if the spectral undead did energy drain more frequently.