1) I'm surprised that you as a neuroscientist make a definitive claim that we need to simulate every atom of our body to ensure that "you" is still "you". Clearly, cutting my nails destructs my persona ;) (Less flippant, it's kind of hard to say which parts of us make us ourselves. I certainly don't see much of a consensus on that)

2) What about the old idea of replacing one neuron at a time with a simulation? (The "Moravec Upload") Caveat: Provided our identity is just defined by our neurons, which is certainly more than up for debate.

3) I'm not aware that there's a claim of exponentially increasing human intelligence for the singularity. The idea is for technology to become self-improving. We'll see about that, but it's certainly a different claim than what you're refuting.