Disclaimer for stockfish in particular: Even if it's mostly bruteforce nowadays, stockfish usually has an edge because it can bruteforce with "taste" and can manage the clock very well knowing when to ponder deeper a position.
> ... search space grows so big that any non-expert will become lost in it.
And I am saying that's a fallacious argument: chess has an enormous search space too, and that does not imply AI can't beat humans.
Also
> You would beat anyone if you could calculate a few thousands moves per second, even more so if you had a neural network that discards suboptimal moves early.
So like the AI can? Your argument's dont add up.
In chess, being able to check hundreds of lines per second makes you a superhuman. But in hardware design you get lost if you try to search the solution space for a circuit, schematic, component selection, layout, routing, stiffener and thermal solution.
There are a few like positioning and routing where the solution space can just be considered infinite as there are infinite copper geometries (even if you stick with straight line polygons) that can connect a number of infinitely differently positioned components.
Then, for the mechanical stiffener, again you have an infinite number of geometries that don't clash with your components, don't run over your copper traces and make the board resist the mechanical tests (which the AI could check with a lengthy FEM analysis per iteration).
After all that, or in parallel with the mechanical analysis you can run the thermal ones and tweak positions of the hot stuff and thickness of stiffener walls to get everything fine.
I just can't see an LLM do that with a board with a few hundred components, even if most are decoupling capacitors.