It's hitting 8%HP - 9%HP against Rotom-W, so you'd want to predict with the Stone Edge if all possible. Why would you suspect a Fire Blast on a Scarf set? I'm just curious.
They might not know you're running a scarf. And you can replace Rotom-W and Fire Blast with whatever else you can think of, the thrust of his argument is that Superpower is consistently powerful, which is what is most valuable on a slow hit and run Poke like TTar.