There is a strong argument that akoya pearls cultured in Japan are always more lustrous than their Chinese counterparts. Some claim it is due to the colder climates. But it would make sense that the thicker nacre of Chinese akoya pearls (nacre deposits at more than twice the rate in China) would make up for this difference. But the real difference is in the processing. Factories in Japan have very good processing techniques which many Chinese factories (not all of them) lack. It really just comes down to the processing. The same goes for freshwater pearls.
