I've been playing around with (GoR'ed) Davanas and Seraphs as supercombatants in my current game. They all get Wraith Crowns as standard equipment. And I've never had one of my SCs flee when all of the skellies die ... ever.
I wonder if it's about hitpoints? My SCs have enough hitpoints that losing a few skellies doesn't make much difference to the total.
Anyway, I'm not saying that y'all are wrong. I'm simply saying that my anecdotal experience doesn't match yours. I hope that helps.
PS: A Seraph with the Harvest Blade and Fenris Pelt can kill a whole lotta chaff in a hurry.
Just remember to bring along someone else (another Seraph?) to bless him, because he won't bless himself.