I think it's warlock for the exact reason you said. Swords just seem like a warlock type of weapon. Rocket launcher, auto rifle, shotgun for Titan because they're meant to be tanks that rush up to your face and end you with foh or shotgun. Handcannons, snipers, and heavy machine guns for hunters because they're supposed to sit back with snipers and stealthily take out opponents or have handcannons because that's a bounty hunter type of weapon and that's what a hunter is supposed to be. Pulse rifles/scouts, fusion rifles, and swords for warlock because they're supposed to have kind of strange weapons like fusion rifles that are futuristic, pulse rifles are just kind of warlock weapons in my opinion, and swords, because of the link with the hive, but also because of the magical sense that the exotic swords have. It seems like a warlocks job to throw an electrical razor like a disc into a group of enemies that brings down a storm on them, or a giant fiery falcon punch.