After thousands of years of research we still don’t fully understand how humans do it, so what reason (besides a sort of naked techno-optimism) is there to believe we will ever be able to replicate the behavior in machines?

>>> But do we have reason to believe that no AI system can synthesize novel technologies

We don’t even know if they want to. But in general, it’s impossible to conclusively prove that something won’t ever happen in the future.

Its not an assumption, it is a fact about how computers function today. LLMs interpolate, they do not extrapolate. Nobody has shown a method to get them to extrapolate. The insistence to the contrary involves an unstated assumption that technological progress towards human-like intelligence is in principle possible. In reality, we do not know.

In the grand scale of things, a computer is not much more than a fancy brick. Certainly it is much closer to a brick than to a human. So the question is more 'why should this particularly fancy brick have abilities that so far we have only encountered in humans?'

That's irrelevant.

The claim being made is not "no computer will ever be able to adapt to and assist us with new technologies as they come out."

The claim being made is "modern LLMs cannot adapt to and assist us with new technologies until there is a large corpus of training data for those technologies."

Today, there exists no AI or similar system that can do what is being described. There is also no credible way forward from what we have to such a system.

Until and unless that changes, either humans are special in this way, or it doesn't matter whether humans are special in this way, depending on how you prefer to look at it.