Why, uh, do people seem to think Dvar and Promethean go together so well? I understand there's some volcanic themeing, and Dvar Promethean units get Plasma Mastery for +20% damage, which is not insignificant, but that's it. The early game Thermal targeting synergy goes for almost everyone else, I think.
Dvar have explosive weapons tree, exclusive to them at the moment, and nothing in the Promethean tree has anything to do with it. The Plasma weapons from Purifiers and Phoenix Walker count as thermal for resistance, but not thermal or laser, kinetic or firearms, Explosive, psy, arc, or bio for the benefits of weapon mods. You have to upgrade damage from within the Promethean damage tree, or not at all. Engineers still suck, even after upgrades, but it feels like Tenchers with range and flechette or fireburst outperform purifiers, even with the bonus damage. Plasmids can take Ironbreaker modifications, but not the Super Powered Pistons mod from later in the Dvar tech tree, and the Phoenix Walker doesn't get any of the melee mods. Though some melee hero skills still proc when in a phoenix walker suit, Dvar don't really get melee hero skills outside of their tech. In order to get max damage out of a Hero in a Phoenix walker suit, you need either to stack +30% damage features from mods that key off your secondary weapons.
Not only that, but the Promethean doctrine that cancels volcanic penalties is somewhat mellowed by the Dvar racial colony building that does the same thing. And all the techs and units that turn a sector volcanic are already in the Dvar tech tree, instead of the promethean.
I'm looking at trying Dvar/Voidtech. It looks like it shores up a bunch of Dvar weaknesses, like speed. The mod to teleport a unit and leave an action point behind seems like it'd work well with many Dvar single-fire shooting and melee attacks, and one of the lategame voidtech vehicles/hero vehicles looks like it benefits from the Firearms tree AND can provide a fast(ish) moving response force.