The South Korean military, including their navy, is not organized, equiped, trained or otherwise intended to be an effective fighting force against the PLA. They exist to fight their North Korean brethren, and arguably to deter the Japanese over disputed territory.
Probably why their first "baby carrier" was christened the Dokdo, after disputed islets controlled by South Korea, but also claimed by Japan:
TBF, while the ROKN doesn't operate nuclear submarines, , or crewed fixed wing aviation from their flattops, in terms of actual capabilities, they're more or less up there with major European powers. Comparatively speaking, they're short on expeditionary capabilities, but unlike the British and French, the South Koreans are also not trying to hang on to distant colonial possessions from a bygone era.
If you look at where the commercial South Korean shipbuilding industry stands globally, it shouldn't surprise anyone that they operate a highly capable navy. Not quite the USN, but definitely a force that should be taken seriously.