I think you are confusing the terms "western" and "american". Not only that your examples of American SF are all TV and film which tends to be even further along that axis than American print SF. Certainly lots of UK science fiction is not about optimism and making the reader feel good.

I have read a few Cixin Lui books and just didn't find them particularly good. The characters are dull and the plots are bad. His proponents tend to go on about him being not being optimistic and him being introspective as though that is a new thing and I just need to open my mind to this new radical way of thinking, but it just isn't new - people like Brian Aldis just did it so much better for me many decades ago.