As someone who lives in a country known for its positive and welcoming attitude towards others, the collective positivity of the US hits different, I feel due to over-commercialization and emphasis on materialistic value, but I don't feel it's an accurate representation of all the existing cultures in the country (but who knows, I've never gone there).
A few weeks ago I watched a video by an asian-canadian youtuber talking about asian fetishization, and a part of her video was dedicated on how some asian countries (China and Japan if I remember) would highlight certain recognizable aspects of their nations and play into the ideas/fantasies historically coined by the West, such as the "spiritual" and "mystic" East, at the expense of misrepresenting the current situation of their countries; this could be with something as small as what their citizens actually wear or live their daily lives. I feel that some of what she said could be applied here, how countries export a digestable and exaggerated version of themselves to captivate the mind of foreigners.
Exportation of cultural practices and values can cement onto the collective mind of the cultures consuming them, and thus, impact their own values and practices. I'd say the influence of US popular culture has become much more apparent in my country's own popular culture with the explosion social media and influencers, but also in conventional older-media such as movies or TV. This isn't necessarily good or bad, but I do feel it's made our cultural identity fuzzier and it's made us not appreciate our own history as much as we should.
As for philosophical pessimism, I don't feel as confident speaking about it due to lack of knowledge, but I feel we have had some of it in my country, particularly in the 20th century, but again, not sure. Maybe the US has a fear of confronting existencial dread and having identity crisis, but I'd argue it's going through one right now with how much shit it stirrs weekly (don't take that comment too seriously).