[rett12]

Korean didn't work at all under the imported Chinese system. Japanese also had problems but they solved inventing the Hiragana, a syllabary system. Both languages chose different systems and both languages work fine.

Also Korean avoids many homophones thanks to it's 10 vowels. Japanese has 5.

[yongjik]

In addition, Korean spelling is heavily morphophonemic, which is a fancy way of saying that words are written based on its "base form" even when the actual sound is different due to interaction with grammatical suffixes.

A bit like English "packed" being written with "-ed" even if it sounds identical to "pact". Helps disambiguation.

(Actually, come to think of it, it's rather analogous to the Japanese way of maintaining the same Kanji while the suffix changes.)

Koreans did have an old writing system[1] made of Chinese characters, where some were used for meaning and others were used to denote Korean suffixes with a similar sound (kinda like how Hiragana started out, I guess). But it eventually died out.

[1] https://en.wikipedia.org/wiki/Idu_script