There is truth to the former, regarding Japan. For example, if you want to see real Tang-style architecture, the only place where you can see them today is in Nara and to an extent Kyoto (all the ones in China are modern reproductions). This is the Byodo-in in Kyoto, built in 998. This is the Chi Lin Monastery in Hong Kong, built in the modern period using the Tang style. You can see that they're remarkably similar. Whereas Chinese architecture underwent several changes as time went on, Japanese architecture stayed very close to the Tang style. Certain Tang customs such as drinking tea in powdered form and sitting/sleeping on the floor are also preserved in Japan, whereas tea leaves and chairs/beds began to become popular in China during the Song.

I really don't understand why one has to go to South Korea to see what China was like in the Ming. If you want to know what it was like in the Ming dynasty, there are plenty of ancient towns in Southern China that had been in existence since the Ming and preserved Ming architectural style.