The Dread Masters were high-level Sith Lords in the Sith Empire.
The Dark Side 'Elite,' on the flip side, were darksiders not given true Sith training by Palpatine.
Dark Empire Luke was able to handle Sedriss, easily the most powerful of them (rivaled perhaps only by Kam), very solidly.
Kam Solusar, another one of them, turned, was able to beat the saber trainer of the group, and temporary hold off three others, and then much later ended up a reasonably strong but not exceptional Jedi master on the council but not one of it's more powerful members, and that's after much more training.
The way Luke took out Xecr Nist, the leader after Sedriss fell (and well after Kam turned), was kinda sad 🙂
Pretty much, of these I think only Sedriss and Kam may be able to put up some fight.
The Dark Side 'Elite' were ultimately expendable tools to Palpatine, and not true elite.