I agree with criticism for 2 assumption. Although I have this intuition (based on possibly very wrong intuitions I have about QM), that argument still works even without it: Imagine same human runs the simulation. Then he goes to another table where he runs spin measuring experiment, with 50/50 probability of getting either up or down. After seeing the result, there is now two different consciousness of him, but there is still just one copy of simulated brains as they did not saw the result.