FWIW, the "extended" Korean PhD is an artifact of grant projects that need people to do the busy work (usually reports), and it seemed to be uncommon to have foreign students thrown into that pool. Scholarship max durations are also a limiting factor.
One aspect worth calling out as a huge plus of Japanese national institutions which the author didn't disclose is funding for compute is much better than what one would get from a Korean institution (e.g. the author's school runs one of the biggest GPU clusters in Japan).
One aspect worth calling out as a huge plus of Japanese national institutions which the author didn't disclose is funding for compute is much better than what one would get from a Korean institution (e.g. the author's school runs one of the biggest GPU clusters in Japan).