>The second of which has a truly mind-boggling number of characters, including every possible composite Hangul glyph used in modern Korean, despite them being constructable from the basic Hangul codepoints.
Also true of most Chinese characters, but the proposal to encode them component-wise was a no-go (for adoption in China IRRC) and separate character encodings was went with in the end. I never managed to dig up the reasons behind it.
What was adopted was an adoption of existing encodings mapping, as per rountrip convertability policy. If Hangul had a working composable encoding, it would've been used instead.
The problem is that Hangul had too many composable encodings from each vendor. As a result the government went to yet another standard (KS X 1001) that fits better to the ISO/IEC 2022 infrastructure. It was too late when the standardized composable encoding was specified as an annex to the original standard in 1992: Windows 95 didn't care about the annex and introduced their own extension to KS X 1001, now known as the code page 949 and standardized in the WHATWG Encoding standard [1].
Also true of most Chinese characters, but the proposal to encode them component-wise was a no-go (for adoption in China IRRC) and separate character encodings was went with in the end. I never managed to dig up the reasons behind it.