Do western artists and corporations borrow stuff from other cultures and competitors? All 20th century rock & roll, most of hollywood, and pretty much all of pre-90s Silicon Valley is based on that premise.

That you think it's theft is a debatable/controversial point of view on Internet forums, but if that is to be the case, many more people/corporations from USA should feel threatened, not just a few chinese scapegoats which help avoid the elephant in the room: why would anyone own ideas in the first place? Ideas are born out of other ideas and every one benefits from that. Restricting knowledge sharing can lead to disastrous outcomes as Jonathan Blow brilliantly argued in a talk called Preventing the collapse of Civilization which appears to pop up on HN every so often: https://www.youtube.com/watch?v=pW-SOdj4Kkk

Um, no, there's a very clear difference between 'borrowing' ideas, building on other people's achievements etc, and outright theft, when you copy someone's detailed designs wholesale, especially from secret proprietary plans obtained through illegal espionage.

This "very clear difference" is the center of many trials in Hollywood / Silicon Valley history so i wouldn't say it's that clearcut. I personally don't see copyright in any way as a mechanism to bring retribution to the creative minds (instead it serves to capture value into big corps and let the artists starve), but as long as we have to deal with it i'll keep publishing stuff as copyleft so that the capitalist vampires think twice before "borrowing" my code.

Do companies hire/recruit (ex-)employees from competitors to re-implement the same features?

Yes.

Lots of IP between your ears. No point in the code/manuals/docs when you wrote them yourself. You’ll know they’re not exactly correct and may appreciate being able rewrite from the ground-up now knowing what you now know.

Sure, but if the employee brings along the architecture documents or the source code, that's theft. What's alleged here is that a CHinese company is exfiltrating actual PCB designs via PnP machine malware.