Here's the mentioned letter: [PDF] https://chinalaborwatch.org/wp-content/uploads/2022/01/Engli...
This would definitely not be as bad in other countries like India where Foxconn is also trying to setup production.
I'm always amazed how cheap and well China can manufacture a wide variety of devices. There is ofc a lot of expertise and economies of scale at work, but the letter is a sad reminder that at least some part comes from exploitation.