It's "useless" in part because, as you note, it assumes Omega works by simulating the player
Or, if you are thinking about it more precisely, it observes that however Omega works, it will be equivalent to Omega simulating the player. It just gives us something our intuitions can grasp at a little easier.
That's a fairly good argument - simulation or something equivalent is the most realistic thing to expect. But since Omega is already several kinds of impossible, if Omega didn't work in a way equivalent to simulating the player it would add minimally to the suspended disbelief. Heck, it might make it easier to believe, depending on the picture - "The impossible often has a kind of integrity to it which the merely improbable lacks."
This problem is roughly isomorphic to the branch of Transparent Newcomb (version 1, version 2) where box B is empty, but it's simpler.
Here's a diagram: