Forgive me if I'm using the wrong terminology for "medieval" Korea. By "medieval" I'm mostly thinking about Joseon post Sejong.
I've read that King Sejong wanted to invent a language that was easy for the average Korean to read, to replace the complex Chinese characters used to write the language. The literati greatly preferred the Chinese and refused to use Hangul for years.
Having learned Hangul myself very quickly, I can understand how Hangul can be thought of as the "dumb man's alphabet" while Chinese is thought of as "higher" due to its complexity. At the same time, I've been reading a lot of Korean stories where it seems like literacy isn't as common in pre-modern Korea as Sejong had hoped it might be.
The literati greatly preferred the Chinese and refused to use Hangul for years.
Just a little clarification: by "years," we are literally talking about 453 years here. Hangul (which was not called Hangul until the early 20th century) was made in 1441:
是月, 上親制諺文二十八字, 其字倣古篆, 分爲初中終聲, 合之然後乃成字, 凡于文字及本國俚語, 皆可得而書, 字雖簡要, 轉換無窮, 是謂《訓民正音》。(from Annals of the Joseon Dynasty, December 30 (lunar calendar, which is a few months faster than the one used in most countries today) of the 25th year of Sejong (mostly 1443).
Source: unfortunately in a mixture of Korean and Classical Chinese
(I don't really want to translate because I'm bad at translating Classical Chinese, but if you want just ask and I'll try to do my best)
However, Hangul did not become an official script until November 1894. So that's 453 years.