China surely was not a small insignificant nation during Cold War. It is a common knowledge in SEA that the communist militia in the region was armed with the Chinese support.
Korea doing it is neither better nor worse than China blocking (some) Korean stuff now.
It is not just entertainment where banning and prejudice occurs. It is across all of Korean society. Some of the most famous food (featured in K-movies/dramas) are Chinese and the Chinese people who developed it in Korea suffered a lot of prejudice.
South Korean has NOT banned Chinese content. It's just the lack of demand. The prejudice is a whole another topic.
But that is more than enough reason to place cultural restrictions on Chinese culture.
Stop the groundless accuse of the Korean restricting Chinese culture.