There is no reason to be happy just because we have become wealthier than Japan.

Because for the past several thousand years, it was only natural for the Korean Peninsula to be wealthier than Japan.
It is true that Japan briefly overtook us for a few hundred years during the early modern period.
However, justice prevails, and things are returning to their rightful place, so from Korea's perspective, this is nothing to make a fuss about.
Regarding GDP itself, it is true that the Japanese archipelago surpassed the Korean Peninsula around the end of the Goryeo and beginning of the Joseon dynasties.
But that does not mean Japan became wealthier than the Korean Peninsula; it was simply that their GDP was higher due to a larger population and more land.
It is just like how China and India are among the top five in the world by GDP, but that doesn't make them the fifth wealthiest countries in the world.
Then, even if they were economically poorer, was the quality of life for the common people good?
Not at all. As you know, Japan was a country that had not established a proper national system until the early modern era.
It was a world of "survival of the fittest" where warlords fought for dominance, a world without law or order where anyone could be killed at a whim.
There is no need to criticize the Japanese trait of "honne" (the difference between one's true feelings and public face), as it was an inevitable survival strategy required to endure such a beastly world.
Furthermore, as Oda Nobunaga once said, "The people must be made so they can neither die nor live," the level of exploitation was terrifying.
It is a famous anecdote that even when Kato Kiyomasa, who invaded Joseon during the Imjin War, offered farmers a much more generous share of their crops than in Japan to win their favor, the peasants were still outraged.
The fact that Japan's ruling class did not treat the common people as human beings is evident from their history of hunting their own people to sell as slaves to Europe.
Then, were they poor and exploitative, yet possessed superior culture and science/technology?
Not even that. It was so dire that during the Imjin War, they were obsessed with looting Joseon's superior cultural heritage, technology, and academic knowledge.
Anyway, there is no end to this story, but I see some people celebrating lately because we surpassed Japan's GDP; let's not do something so embarrassing.
Japan was never our competitor or even an object of interest to begin with.
It is only natural that the Korean Peninsula is the wealthier one.