What you are implicitly describing is called a phonemic orthography and it has a well-known share of problems. Fully phonemic orthography means that any pronunc

What you are implicitly describing is called a phonemic orthography and it has a well-known share of problems. Fully phonemic orthography means that any pronunciation difference should be more or less reflected to that, but that means all dialects of a single language should be recorded differently. Also many such differences are linguistically transparent, that is, native speakers actually don't really realize and so can't really distinguish them. Therefore it is desirable to weaken the phonemicity a bit to make it more palatable for native speakers. Hangul was originally highly phonemic, but a modern reform is much more hybrid ("morphophonemic") mainly because it's much easier and relatively more stable in the long term. Double letters, for example, are used when a syllable coda (jongseong) affects the following syllable onset (choseong). Such cases can be quite regularly described as having two codas, where the first coda remains in the original syllable and the second coda is merged to the following syllable in a specific way. The actual difficulty in the Korean language is much more subtle than that in my knowledge.