Okay, your second paragraph confuses the hell out of me. It sounds like you're arguing against yourself. Can you rephrase it for me? I want to understand what you're saying.

Also, the US doesn't have an emperor. It may be imperialistic, but it's not an empire. But reading that makes me imagine it as an actual empire, which is fucking terrifying. Please don't? At least for me? That makes me wildly uncomfortable.

So... The US occupied the South until the ROK was established. This was kind of like Germany but for a much shorter time. When the North invaded the South, UN forces came to help. Yes, there was a direct line from Japanese occupation to US occupation, but US occupation ended very shortly afterwards. Say what you will about influence, but influence and occupation are very distinct. And yes, the US fucking with the PRK was terrible. I'm with you on that. But we're talking about South Korea today.

But going back to the original point, if the societal pressure results from the US, then why don't we see such pressure in the US itself? Your historical argument for this doesn't stand.

A simpler explanation is the rise of Neo-Confucianism during the Joseon dynasty. It was patriarchal, focused on hierarchical structures, and expected testing for advancement. This clearly leads to competitive behaviors. While you could argue the US has similar things, Neo-Confucianism cranked that up to 11. The Joseon dynasty after Sejong was pretty shit. Korea was like this before the US showed up, even before the Japanese showed up (the last time. They tried so many times before that).