I don't see how Singaporean looks much different from those Chinese since 73% Singapore population are Chinese. Same as Tibetan and Burmese they are genetically closer to Chinese than Korean. So, you expect that Chinese looks more like Korean than Singaporean, Tibetan, and Burmese from SEA? Is that your argument? Laughable.
I have not mentioned Thai, the majority of their population are Tai. They are closest to those Tai, Zhuang Yunnan which now part of China, and assimilated considered as Chinese.
To me, when someone mentioned about East Asian, are those come from East part of Asia included Mongolia and Taiwan and not Vietnam, Singapore, Indonesia, Philippines ...etc. How these people look not any unique than those who live in certain countries in South East Asia.
When talking about the term East Asia/East Asian, try to set your mind the geographical the people live rather than how the people look.
I still have no idea what point you are trying to make with Singapore, Tibet and Burma. All those people could be related to Chinese more than Koreans but that still doesn’t change the fact that foreign idols in K-ent are mainly Chinese (and Japanese) because they are close in looks and culture. If you don’t want to call it East Asia, it is up to you.
The natural affinity is there so the interactions between Korea and China/Japan is many multiples greater than those with SEA whether it is business, education or entertainment.
Again, with Thais, Korea is diversifying anyways. East Asia as a whole is diversifying. China has two Thais in its nation gg.
Instead of complaining about some “superiority” bullshit that no one brought up (except you) the growing number of Thais in East Asian puts lie to your paranoia. If the looks and market value are there then Korea will accept them.