The physics of our brains can in principle be simulated at a subatomic quantum level mathematically, even on a classical computer. It would be absurdly expensive and slow with current technology, but it is mathematically possible. Therefore our own generally intelligent brains can be considered a counterexample. I think for your theory to hold up, you would need to show that physics cannot, even in principle, be simu…
AGI is clearly possible, because our brains are fundamentally machines, and there’s no reason in principle why we couldn’t build something similar. Right now we don’t - as human beings - have the ability to do that, but it clearly isn’t impossible since cellular machinery is able to build it in the first place.