I agree with the list given geopolitical aspect of it. In the region Israel could decimate all of it neighbors at the same time in short order if they had the will. In SE Asia SK is very strong, if the entire concept of strength being "pratice" then the only country worth it's weight in arms is the US which is not the case.
Could SK defeat the North? Not without the help of the US, but they also do not have a million man army and 10k batteries of artillery pointed at the NK capital. If anything the US has made them weak by staying there. We should just treat them like Israel if anything.
The problems with just leaving them is that Russia, China, and N. Korea would have a powerful influence over them. They don't trust Japan so they may succumb to that influence. Also, S. Korea is our beachhead into East Asia. It is an extremely valuable property.