Well, your reasoning appears to be, "A simulation of our universe would require vastly immense computational resources. Things that require vastly immense computational resources are vanishingly unlikely. Therefore, the existence of a simulation of our universe is vanishingly unlikely." I can't think of an argument for the second premise.
ETA: well, I can think of one argument: "A universe with vastly immense computational resources would have a very high Kolmogorov complexity." This is false, however, as, for example, Conway's Game of Life seeded with a normal number in Z-order) will compute everything that can be computed.
Not just "vastly immense", but "on a fundamental level, more than exists in our universe, by a factor which is almost certainly greater than zero and whose natural scale is potentially vastly immense".
If you want to argue that the simulation is happening in a different universe, then by that same argument, that is a universe with a lot more stuff going on in it overall than this one, and so the question becomes, why, from an anthropic perspective, aren't we experiencing that one? Which is a weak argument, because if both exist, then SOM...
I've written a prior post about how I think that the Everett branching factor of reality dominates that of any plausible simulation, whether the latter is run on a Von Neumann machine, on a quantum machine, or on some hybrid; and thus the probability and utility weight that should be assigned to simulations in general is negligible. I also argued that the fact that we live in an apparently quantum-branching world could be construed as weak anthropic evidence for this idea. My prior post was down-modded into oblivion for reasons that are not relevant here (style, etc.) If I were to replace this text you're reading with a version of that idea which was more fully-argued, but still stylistically-neutral (unlike my prior post), would people be interested?