There is no fundamental barrier to AI cognition that we know of. But we don't have any proof that superhuman intelligence is even possible at this point. It could be algorithmically limited in ways we haven't discovered yet.
Full brain emulation is probably possible, but we don't know if it will be cost efficient compared to baseline humans.
Likewise AIs smarter than humans might be possible, but we don't know what the tradeoffs would be. Maybe they will lose coherence at larger scales. Maybe they will have high levels of goal drift making them functionally useless.
The other thing to consider is that the universe is still very very young vs our best estimates of its lifespan. We are roughly 14 Billion years into something that may very well be going for 100 Trillion years or more.
You're really just making an even more extreme assumption - that human cognition is the peak possible intelligence - biological or technological - based on zero evidence.
It's much more reasonable to assume we are not perfect and maximally intelligent.
Full brain emulation is probably possible, but we don't know if it will be cost efficient compared to baseline humans.
Likewise AIs smarter than humans might be possible, but we don't know what the tradeoffs would be. Maybe they will lose coherence at larger scales. Maybe they will have high levels of goal drift making them functionally useless.
The other thing to consider is that the universe is still very very young vs our best estimates of its lifespan. We are roughly 14 Billion years into something that may very well be going for 100 Trillion years or more.