Guess #3, this time with some wacky/dumb/maybe logical ideas:
Soldier + Oathkeeper = Warlord
Nightblade + Oathkeeper = Dervish
Demolitionist + Oathkeeper = Shieldbreaker
Occultist + Oathkeeper = Sentinel
Arcanist + Oathkeeper = Templar
Shaman + Oathkeeper = Archon
Inquisitor + Oathkeeper = Paladin
Necromancer + Oathkeeper = Oppressor
Edit: Note to self, don’t make guesses when I’m barely awake.