Koreans obviously have more Han Chinese blood and genes because they were conquered by the Chinese many times in their history (ie Han, Tang, Ming Dynasties), but the Japanese also have 45% of this Chinese genes (Y chromosome haplotype which is passed on paternally). It is sure bet that Yayoi has some origins in China.
With these findings I don't think it is proper for Koreans and Japanese to look down on the Chinese. Afterall, they are all the same.