We already know a warlock who got corrupted by the hive, and he definitely didn't go around murdering people with a handcannon. Warlocks are classier than that. Toland went into the ascendant realm, Osiris went into the Vex gate system. I feel like Yor doesn't fit the psych profile of a warlock. Also, a titan would probably just smash some skulls in rather than use some poisoned bullets.