I use my special weapon against bosses 80% of the time. The ease of sniping adds without having to worry about dying and fusion rifle blasting tougher enemies who would wreck me if I got into usable shotgun range is just better. Bosses usually 1 shot you if you get close enough to hit them effectively with a shotgun. Also, when they multiply the damage by 2, they are FURTHER reducing the shotgun effective range. Shotguns will still only be usable against trash that you can kill faster with your primary. Except for minotaurs. Boy are minotaurs boned.