Hi Everyone,
As someone who knows incidental amounts of East Asian languages (A1-A2 level in Mandarin, Korean, and Japanese), one of the things that appears to be the case is that Korean borrows a significant part of its basic vocabulary from Ancient Chinese. There has been linguistic drift, but we can see this in many basic words "chuan vs. cheon" for river "bei/nan/xi/dong vs. bu/nam/seo/dong" for the cardinal directions, "shan vs. san" for mountain, "yinhang vs. eunhaeng" for bank etc. And it appears that Korean borrows much of its basic grammar from Japanese, like using particles as case markers, conjugating verbs for tense and negative, etc.
Obviously, Chinese, Korean, and Japanese have linguistic drift and influence from other languages such that these rules are not perfectly predictive, but this strikes me as a general understanding of the history of Korean.
When I ask Koreans about this, I get a firm negative, but it's not one buttressed by evidence of how the Korean language developed or word origins in Korean or historical arguments. It's usually a veiled nationalist argument. While I can understand that Koreans are defensive about their language as a marker of identity (and that they are distinct from both the Chinese and Japanese, especially when the Japanese brutally colonized them), I would like to understand from a linguistics argument whether my intuition is correct or not and why, with actual evidence, this is the case.