I'm not TorB
Did someone summon me?
For starters, it would depend on how you define two dark players. I mean, I probably qualify as a Darkness player, but that's not to say all my decks are Darkness decks...
And even when considering two Darkness decks, there are many possibilities. If one of them is a Devourer-based denial deck and the other is not built with facing denial in mind, the denial will probably win. If both of them are Devourer-based denial decks, the starting hand will often have a huge impact on whom gets locked down. If neither side is using Devourer-based denial, you will probably not play Dusk Mantle or Vampire Dagger unless your opponent also has one in their slot, or you can Steal it back. Preferably more than once if you are expecting Steals. If you play it when you can Steal it back, yeah, expect that permanent to change ownership until another permanent is played or someone runs out of Steals. Leaving your opponent with a Dusk Mantle/Vampire Dagger is just too annoying.
Devourers without off-element cards to go with them don't really make for a true denial deck, so then quanta could potentially go back and forth, causing both sides to get less quanta than they might expect when facing decks without. But it's inconsequential, really.
Deck builds are the most important part, especially keeping in mind whether or not the opponent expects another Darkness deck. You could even do a rush deck with Gargoyles, Black Dragons, excess quanta, no permanents worth Stealing and no Devourers. This could outrush denial decks, while rendering the opponents' Devourers and Steals relatively useless.
