Confucianism and ageism existed far before the 19th century, the fact is that Chosun dynasty was the result of a military coup when the general tasked with attacking a weakened the neighbor Yuan dynasty (China) struggled to maintain legitimacy and thus forced upon a new state religion called Confucianism that ousted Buddhism. It was under this system rigid hierarchies regarding one's class, education, ageism were enforced. You can see the difference from the earlier Korean kingdoms like Silla that imported and cultivated Buddhism leading to female rulers and greater tolerance for "LGBT".
Chosun was rife with corruption, rigid social hierarchy except through state examinations one could join the ranks based on skill and stability. It was very stable because of the oppressive social hierarchy based on neo-confucian ideals. The royalty were corrupt and immoral (with the exception of Sejong who created the Korean alphabet) and the last Chosun queen herself spent most of the state's treasury on luxury goods.
Not many missed the Chosun dynasty, well apart from North Korea which introduced many of its traditions (punishing 3 family generations of state designated criminals is from this era), ageism, caste, oppression of women, sexual minorities and male chauvinism. In fact Japan's colonialism brought more equality and ended caste system with meritocracy. Any modern claims of "collaborators" or such are moot, because it was a failed monarchy state and Korea simply was without any political direction.
Korea's success is economic success is largely owed to the Japan (the first capital investments and transfer of technology was from Japan to normalize relations) and its imperial economic system of zaibatsu (chaebol) and the 5-year economic plan that the strongman Park Chung Hee used was straight out of Manchukuo.
anyways just rambling on here as I eat pistachios about my understanding of korean history as an outsider on a friday evening.
y'all have a good weekend.