Your defense stat is wrong here. Skarm won't have less than 300 Def unless you have a terrible Def IV or something. On specially defensive Skarm (Impish with no Def EV):
864 Atk vs 347 Def & 334 HP (120 Base Power): 207 - 245 (61.98% - 73.35%)
Specially Defensive Skarm is listed as Carfeul being the primary nature, although yes the defense stat is wrong. I looked at the "min" and added 31 IVs forgetting about the nature reduction. Regardless taking out that kind of chunk from Skarm with a resisted Physical move is damn impressive, especially when it can shut down Whirlwind with Taunt and basically nothing else in the game can swap into it:
864 Atk vs 316 Def & 334 HP (120 Base Power): 229 - 270 (68.56% - 80.84%) Careful SpDef Skarm
Also @SJCrew: The thing about Onono is that it's literally the
perfect Double Dragon Poke. It breaks bulky waters and Steel types easily, and when well support Double dragon works amazingly well. Dragonite + Mence isn't the best example, Kingdra and Mence were used together as well as were Mence and Latias despite being on opposite sides of the spectrum.
The point that I was trying to make is that people are
exclusively comparing him to other Dragons which doesn't make sense to me. Not only because you can't just say "DD is outclassed by Mence" or "SD is outclassed by Chomp" because he has
both, just like how in Gen 4 terms, DDMence wasn't broken alone, and MixMence wasn't broken alone, but that Mence could be either made him extremely destructive. Onono can viably be DD, SD, Banded, Scarfed, and can hold Haban, Yache, or Life Orb in his set up sets. He's versatile so directly comparing DD to DD and SD to SD really gets you nowhere fast. In addition to that, comparing Dragon to Dragon forgets taking into consideration the metagame surrounding the Dragons and while this may or may not change were Onono stand ni relation to them, simply saying "Mence/Chomp/Flygon outclasses it" seems dumb.