How will they work as a dwarf subclass? Are they going to get proficiencies to axes and hammers and poison resistance PLUS the Duergar Magic and resistance to Charm and Stun? If Larian bundles all those bonuses together, I'd assume that Duergars won't get a stat bonus beyond the generic Dwarf ones, unlike the Gold and Shield Dwarves.
You might have some clues here :
Duergar statsIt is supposed to be PLUS indeed