sure but we haven't even started to define what constitutes a valid simulation. That's half of the point here, we're trying to recreate something that we don't know.
That's true. The big if is whether we can ever have the resources to fully simulate the human brain. If we ever get close to that, then we can worry about the "intelligence explosion" and so on. It feels very possible that we'd work out how the human brain works at some point, though.