The premise is debatable. Let’s take an unbiased look at the achievements of each country in the last 20 years:
China since 1999:
-Has lifted millions out of poverty
-Sustained enormous YoY GDP growth under Hu Jintao and Xi Jinping
-Hosted their first Olympics
-Rose up to surpass Japan as the world’s second largest economy
-Has technologically caught up to both Japan and SK with high speed bullet trains, 5G wireless technology and smartphone technology
-Now has the world’s second largest military budget after the USA
-Dominated the economically developing world with initiatives in SE asia, middle east + africa with the 1B1R initiative
-Owns a significant portion of the Hollywood industry: Legendary Pictures for example is wholly owned by a Chinese company
-Boasts the world’s second largest tech startup scene after Silicon Valley in the USA
-Has the world’s second most billionaires after the USA
-Chinese brands like Lenovo, Huawei, Oppo, Xiaomi, ZTE, DJI, Hisense, etc have risen up and overtaken Korean/Japanese brands
-Approval rate of Xi Jinping at over 85%
-China global approval rating has surpassed the USA
South Korea since 1999:
-GDP/capita remains the fourth highest in Asia, after Singapore, Japan and ROC (Taiwan)
-Economy was hugely impacted by the 1997 Asian Financial Crisis; since then the economy has been growing but at a far slower rate than China has
-Technology wise, Samsung and LG have overtaken Japanese brands Sharp, Sony, Panasonic, JVC, Pioneer, Toshiba, Fujitsu, NEC etc and essentially pushed them out of the market. Hyundai and Kia have caught up to Toyota, Honda and Nissan with regards to quality perception.
-Continues to develop great public infrastructure, the fastest internet speeds in the world and free public wifi anywhere
-Minimum wage increased but unemployment rate, especially for the youth, continues to lag behind other developed countries
-Startup scene in South Korea is still quite anemic due to the remnants of the conservative Chaebol culture which continues to dominate the South Korea work industry; this makes it wary for investors to offer venture capital, and more difficult for small companies to compete which leads to the unemployment rate situation above
-Moon Jae In (President of SK) approval rating at a mere 45%– Koreans have rarely sustained high approval ratings for their Presidents due to corruption, scandals, and the generally more conservative society
-Korean entertainment scene has exploded and KPop and KDramas and ‘Hallyu’ has made Korea into one of the most popular entertainment juggernauts in the world
So back to the OP’s question, is South Korea really more advanced and successful than China? Perhaps in only a few areas.
-GDP/Capita -> China is catching up on this front, but the reason SK had a huge head start is because they had a market economy for 2 decades longer than China did, and because SK was one of the four East Asian Tigers (all small East Asian countries), it developed very fast in the 70s-90s, China had to struggle under the Mao era for 2 decades.
-Entertainment industry -> China’s heavy handed approach to censorship kind of handicaps them in this area, but China’s entertainment industry is mostly domestic focused. They have such a big domestic market that they don’t need to export that industry yet. South Korea on the other hand, has to export in order to survive, and they’ve perfected the art of marketing to foreigners at this point, which is why they have succeeded so well with their Hallyu industry. It’s worth to mention that China owns many Hollywood studios as well, which also means they don’t need to necessarily export their own movies; they can just leverage Hollywood movies to make money.
In the economic, business and technology sense, China has caught up and/or exceeded Korea.