Very good points. I wasn't trying to make assumptions about our relative sentience, only to point out the key assumptions that the argument takes for granted.
I don't think that we're in a simulation, but whether certain modes of thought are inherent or accidental definitely influences the probabilities.
Since we have so few data points, we can't possibly conjecture. And Elon musk didn't even calculate the actual path of a space roadster correctly. Why would we credit his simulation probabilities?