You made some solid arguments for everything but if you don't mind for making this post easier to read I'll just quote the last line. But I read everything and you made some solid points.
The thing is (I knew it could Volt Switch...As you said, for some reason neither of us know) but at that point you're just running an Spinless Iron Treads that can't booster and without potential Ice Coverage. I don't think that Cobalion is completely useless, like dead weight in every game (as I said, I do think it wins teraless Gambit and it can check and cripple Dragonite) but the "role compression" it brings it's not worth and it has really bad matchups aganist a lot of top tiers.
You can, as you correctly stated, slot Heavy Slam, and Volt Switch, but at that point you're using Iron Treads 0.5