They're both solid for add clearing, but they have different functions beyond that. Juju synergizes best with super-focused playstyles + super-enhancing exotic armor. Outbreak is just a great all-around primary that can also shred powerful enemies when you start stacking nanites. Sadly, they both stop being useful in late endgame PvE where champions and shields start becoming obnoxious. You COULD use the unstoppable pulse armor mod, but why do that when you can just slap unstoppable onto a legendary weapon and save your exotic slot for Xeno/Anarchy/Izanagi's?