I mean, to put it very bluntly, the Koreans I know and have discussed this with all think their country is just better than China. Culturally, commercially, politically... It's like Americans thinking they're the beacon of liberty in the world.

Korea has developed faster than China in the last few decades and hence is now considered a developed nation. Nevertheless, much of this mentality comes from being the underdog in the region - a mouse beside a sleeping dragon.

Here is an academic paper regarding the potential pivot. Basically comes down to this:

Historically, Korea has tended to side with the most powerful state in Asia. Until the end of the nineteenth century, China, for the most part, was East Asia’s hegemon. Following independence from Japan after World War II, and in the context of the Cold War, South Korea turned to the United States. Debates among South Korean political elites have vacillated between dependence on the U.S. alliance and the desire to pursue more autonomy. Today, South Korea is hedging against China’s rising influence by strengthening the U.S.-ROK alliance while developing friendly ties with China to prepare for a possible U.S. retrenchment. Strategic debates among South Koreans in the coming years will center on whether staying with their default foreign policy of a close alliance with the United States will help or hinder peace and security in Asia. While the overall dynamics in the region will greatly depend on the state of U.S.- China relations, South Korean choices will also matter.