They would whoop the JMSDF and PLAN's arses!
They have a good high-tech navy but lacks of many things that are key to be the most powerfull navy in this region.
1. Aircraft carriers for power projection.
2. Nuclear submarines and underwater launched missiles.
3. LACM (like Tomahawk, eg. Iraq war).
4. Large LPD.
5. Huge number of advanced DDG, stealth FFG and corvettes.
6. 21st century warfare tools like satellites for tracking & sea recon, netcentric warfare, long range air-defense, supersonic stealthy AShM etc.
SK is pretty good in points 5 and 6 but far behind in other key tools.............