Looks like these are the last of my Destiny art that I have, they were drawn a good while ago. Definitely 2020 if not 2019. They were just early concepts but regardless even today they still apply to Nova, Azazel, and Adam-17.
Warlock: Initially called Duskblade (now Willstealer), this Darkness subclass commands the power of the Taken. The Super acts like a dark version of Daybreak, with the ability to fire out slashes from the sword, but also allows the ability to fire Axion Bolts from the free hand an even slam into the ground to deal heavy damage.
Hunter: Initially called Venomstrafer (now Venomstalker, or Wraith), this Darkness subclass harnesses the power of Hive soulfire and its toxic effects. The Super involves wielding corrosive blades that can be thrown and will boomerang back to you, or can be used to slash away at combatants, spreading noxious poison through the enemy.
Titan: Lazily initially called SIVA (now more appropriately renamed to Replicator), this Darkness subclass combines the power of SIVA with Guardians' paracausality. The Super involves wielding a nanite-forged battle axe, which can then be used to spread more nanites across the field to aid you in battle.
I have since refined the 3 subclasses (and even added 2 more SIVA-based subclasses for the Warlock & Hunter, + a Nightmare subclass for Titan), but I'll show those off whenever I get around to them :)