Lot of Korean youth wanna leave because they want a less stressing and competitive life style. Also, SK geopolitical situation is pretty delicate which adds to the stress. USA still has a decent reputation overall with Koreans (negative views on USA seems to be very eurocentric POV) and Korean community is sizable which helps with relocation. Probably Australia and Canada are becoming more appealing options than USA lately thou.
Still this is just wishes and perception. Looking at migration stats (net migration and raw numbers of migrants leaving), not that many South Koreans migrated really over the years. Comparing it to Poland (comparable size and geopolitics), less South Koreans left SK than Poland. Not sure why TC singled out SK when other decent nations also suffer for that (like Balkans in EU). SK is more a perception problem in comparison than reality.
Now about topic creator's "idea", I have no idea what you are on. Even if South Koreans complain and wish about leaving, they aren't leaving in droves (at least to be relevant stats wise). It seems to be just perception and an opinion not fueled on data and just based on anecdotes (I have relatives who also say this shit, but they are mostly just babbling). Sure Hell Joseon is a thing, but actually leaving is a different matter. The proposed "solution" is just a dumb idea and not based on reality (the Singapore example is really off). SK doesn't need help in this regard. They just need to improve their geopolitical situation and start adopting practices and mentality that improve school and workplace life.
you comparing by population?
because by land South Korea is really small, smaller than Bulgaria, similar to Iceland, and bit bigger than Hungary or Portugal...
on the other hand by population it's hard to compare because they are very similar to Colombia, and have a bit 3-4 mln people more than Spain.
It's normal that people in EU migrate, because it's easy here, as you mentioned Poland then the way Poles move to Germany the same way Ukrainians come to Poland.
