shell smash smeargle is really bad, even at +2 you're still incredibly weak and almost always need tera to kill something (sometimes tera isn't even enough) and despite being high level and having spore i still find it incredibly hard to even get a shell smash off as it still dies to pretty much everything. i get you're trying to branch out sets for mons but i feel like this set actively hurts the mon, it's just a worse maushold
If you want some insight as to how we look at damage calcs, we normally test everything on a normal type arcanine for damage. Generally we consider something strong if it can do 50% or greater to arcanine; for example:
Lvl 86 84 Atk Choice Band Mabosstiff Crunch vs. Lvl 84 84 HP / 84 Def Tera Normal Arcanine: 154-183 (53.4 - 63.5%) -- guaranteed 2HKO
With that said, here's the calc's of smeargle vs every other shell smasher in the format, as well as some ridiculously strong attacks
+2 Lvl 95 84 Atk Technician Smeargle Population Bomb (10 hits) vs. Lvl 84 84 HP / 84 Def Arcanine: 330-390 (114.5 - 135.4%) -- guaranteed OHKO
+2 Lvl 79 84 Atk Cloyster Icicle Spear (5 hits) vs. Lvl 84 84 HP / 84 Def Tera Normal Arcanine: 230-275 (79.8 - 95.4%) -- approx. 2HKO
Lvl 84 84 Atk Choice Band Slaking Double-Edge vs. Lvl 84 84 HP / 84 Def Tera Normal Arcanine: 280-330 (97.2 - 114.5%) -- 81.3% chance to OHKO
+2 Lvl 80 84 SpA Torrent Blastoise Hydro Pump vs. Lvl 84 84 HP / 84 SpD Tera Normal Arcanine: 286-337 (99.3 - 117%) -- 93.8% chance to OHKO
+2 Lvl 81 84 Atk Drednaw Stone Edge vs. Lvl 84 84 HP / 84 Def Tera Normal Arcanine: 222-262 (77 - 90.9%) -- guaranteed 2HKO
+2 Lvl 79 84 SpA Polteageist Shadow Ball vs. Lvl 84 84 HP / 84 SpD Arcanine: 190-225 (65.9 - 78.1%) -- guaranteed 2HKO
+2 Lvl 78 84 Atk Torterra Headlong Rush vs. Lvl 84 84 HP / 84 Def Tera Normal Arcanine: 238-282 (82.6 - 97.9%) -- guaranteed 2HKO
+2 Lvl 95 84 SpA Magcargo Fire Blast vs. Lvl 84 84 HP / 84 SpD Tera Normal Arcanine: 277-327 (96.1 - 113.5%) -- 75% chance to OHKO
As you can see, smeargle does more raw damage than every other shell smasher, even outdamaging choice band slaking double edge
You also mentioned maushold, and after one turn of setup we can see that they do the exact same damage, and I'd argue that smeargle is more of a sidegrade since you don't get the hazard clearing effect, but in exchange you get stronger dark coverage + spore
+1 Lvl 76 84 Atk Technician Maushold Population Bomb (10 hits) vs. Lvl 84 84 HP / 84 Def Tera Normal Arcanine: 330-390 (114.5 - 135.4%) -- guaranteed OHKO
I get that setting up a shell smash can be hard in a lot of scenarios, but looking at the raw damage we decided it would be worth testing. Cake already touched on the stats part, and if the winrate ends up dropping we will look into reverting the set, but I hope this provided some insight as to how we build sets what damage benchmarks we look for. If you have any other questions with how sets work, either check out the
rands explainer thread, or ask here, and I'd love to help answer them! Sorry this ended up being quite a read, there were way more shell smashers this gen than I thought lol