Bungie generally gives certain types of weapons to classes. Hunters hand cannons, bows, sidearms, and glaive. Titans all things related to automatic fire and explosive (not including perks) Warlocks, fusion, linear, and trace. Likely in the future scout will be added. They'll likely never add a titan bow exotic (not including things like path which buffs solar weapons since its not specificly for certain weapons). Maybe crossbow because that works differently but id wager it'll go to Hunter.