As a Korean I have to point out western view on these kind of problem comes from very narrow perspective that only revolves around western social background. I can only speak for Korea but from my impression even though KR/CN/JP's political relationship is fucked up and we hate each other it seems the hate against government/politics is well separated from the individuals or the culture in general. That's because these countries are heavily influenced by each others culture that goes way back from the modern days and also their demographics are all homogeneous so there isn't a good amount of people to make a voice with in the society. Even though they did it is very easy to be undistinguisable with a time span of one generation. This is what happened to most of the Chinese in Korea or Koreans in Japan. They just naturally assimilated to the majority. Of course there can be a small group of people (especially between Korea and Japan) that seems to be toxic but it's far from what the GP has in mind. I mean at least in Korea it is. But when I see how some Korean celebrities are loved in Japan and China I assume it is similar. I mean to be very frank in some of the cases I can totally see that it even works as an advantage for them because Korea loves foreigners that love and respect Korea in general. But I will admit that it would be very ugly when they got involved in politics thats for sure.

Meanwhile in the west the political climate is very different because they are mostly multi-cultural and discrimination comes with deeper implications. So it is very obvious even the most subtle racism is viewed more seriously and I respect that. However people have to acknowledge that it isn't always the case in other countries. The way I see it is that racism comes from hate and it is really hard to hate somebody when you don't have them in your area and don't cause any socially impactful agenda.

In short, there really isn't a noticeable hatred towards idols that came from Japan or China because of the nationality unless they have been associated with politics. Also I have to say this kind narrative only comes from the idea that westerners see k-pop industry with a lens of western society that k-pop industry somehow being the equivalent of hollywood. But unlike hollywood K-pop is eccencaily a Korean industry and they don't have any obligation to represent anyone outside of Korea in the first place. Also I can only imagine these kind of blatant assumption that Korea isn't open to the idea foriegners having a place in k-pop comes from these kind of projection. Plus the k-pop groups that have those foreign members are also heavily focused on those market as well and Korean member in those groups have to play around the same dynamics of being a foreigner in Japan or China too so they are not the only one that goes through this. For example famously BTS has experienced the same kind of issues you mentioned both in Japan and China. After all Japanese and Chinese idols are the majority in their own countries and they are still heavily promoting in their own regions too so what kind of oppression are we talking about here.