Ancient Skull or Devouring Diadem for BAMA?

So far I have used the Ancient Skull on my BAMA Voltaxic Necro but I see most builds choosing Devouring Diadem instead plus spectres (which won't stay alive with the Skull). It seems to make sense because you use a lot of points to get to Eldritch Battery otherwise but when I change my POB and use those extra skill points for a (very expensive) cluster then the damage seems to be basically the same. And that is assuming that both spectres are alive and frenzy/power charges are fully up. Am I missing anything that POB is not telling me? Should I just stick with Ancient Skull and use the minion sockets otherwise?