Beelzebub slots D/D Haku really well (She is a great sub for any dark devil teams). I love using my Ronia, and Teaming with an Ultimate Beelzebub is just easy street for some descends. It is like running the old 2/4/2 mono color teams of old. The main difference is that when paired with a Ronia, you can use her active to get the row attacks which add so much to the damage. Not sure if Pandora is a Devil, but if she is it may make sense to work on her as well.
Awoken Minerva - Minerva is practically worthless without being awoken, however once awoken she can be very useful on a devil team, even a dark focused one, if you need armor break (50% saved my butt on an enormous Metal Dragon invade). Having a good multiplier AND the 50% damage reduction is just icing on the cake. I max skilled her, used two Flampy's to do it.
I am a strong believer in the devil teams, makes farming easy, and works through a lot of descends. As far as the new "TOP" descends, you may need to hold out hope on a 25x+ lead. I know I have had to skip some descends because I just can't do them (still can't do Hera Rush and most of the top challenges).
Thanks.
Problem with the Devil team is that I don't have Lu Bu, Persephone or Hades though.