Good points. The chances of us being a simulation falls below 50-50 to low odds if we consider the "lousy" natural selection by "no design" - no woman who underwent labor would say that it is an excellent "design" by a simulator (whatever entity simulated us) - not that I would know (being a man). And mammalian anatomy is replete with examples of "bad desgin" by "natural selection". Of course, that would still not invalidate the simulation argument - bad design or not. It would make the odds of us being simulated by an entity approach closer to zero.

I also hasten to add that the products of our (human) design (von Neumann architecture for instance) is far superior than any natural design and much closer to rationality. The blind watchmaker indeed came through and culminated with homo sapiens, but our designs far outsmart the "simulators" of us and our universe. Like Feynman said, what a waste - when virtual particles just emerge and dissolve into the void of spacetime. Just all these facets must be considered before making a solid case for simulation.