The other appeal of Gorebyss is that it is free to use its item slot on White Herb, while Smeargle is stuck with Focus Sash. White Herb makes baton passing the boosts a whole lot easier and it makes your sweeper much less susceptible to priority. I don't understand why you are downplaying the extra bulk and the offeensive presence though, they are a pretty big deal. Gorebyss can force out more targets than Smeargle, even with Spore, which makes it have more set up opportunities and harder to phaze. Spore Smash Pass Smeargle can actually be phazed by Overcoat Mandibuzz, Roar Venusaur, or Perish Song Celebi.