There are some lovely old churches and cathedrals in Korea. I’m not sure that the Cathedral in Pusan would qualify. Namcheon Cathedral, whose titular saint is St. Paul Chong Ha-sang, is a quite modern building. While it is definitely big enough to accomodate large crowds for major diocesan occasions, such as the recent episcopal ordination of the Auxiliary Bishop Joseph Son Sam-seok, it exemplifies quite possibly the worst of brutalist architecture.
Many bad things happened in the 1970s, the Carter presidency being among them. It was not a good time for architecture.
Here is the exterior of Namcheon Cathedral.
I found an image of the interior which I downloaded from the Cathedral webpage.