- we don't understand enough about the brain to emulate it.

- we don't know how to model the brain.

- even assuming we had the required scientific knowledge, there would likely be major engineering problems.

So, in other words, it's not impossible in the same sense FTL travel is not impossible, our scientific understanding does not categorically exclude it, but making predictions as to when it will happen is kind of silly, because it will likely require several fundamentally unpredictable scientific breakthroughs.

Square-cube law. As the number of processors grow how do you hook them together? If you want to minimize latency you end up with a solid packed sphere. O(cube root) latency. In that situation, heat dissipation only scales with the surface area of that sphere. So there is a limit to the scale. If you choose a topology that permits cooling, then you accept ever increasing inter-processor latency which eventually bottlenecks your computation.

Computers are not magic. They exist in a physical reality and have to deal with thermodynamics and the speed of light. Just because we feel like we have a lot of them doesn't mean we have enough for "magical super AI" to work.

Well, neither is there any reason we know that it's possible.

You're just demonstrating your apriori biases ("the brain is just a computer"), nothing more.

P.S. If we presume that human intelligence is a random processes, then there's no reason to think that this random process can create another that has more information complexity than the original. It makes no sense mathematically.