I am a native Russian speaker and a former Korean language major. I would estimate that the modern Korean writing system has roughly the same amount of exceptions and non-phonetic spellings as the Russian one.
For example, the letter ㅎ (h) is not pronounced in a lot of cases. Some other consonants are reduced depending on their position in the syllable, etc.
The illusion that Korean is "pronounced as written" is created by the fact that Koreans are extremely happy when you learn to speak their language at all. I as a Russian speaker would also rather hear you pronounce Russian words as they are written than not try to learn Russian at all :) But as soon as you start working on sounding as close to native as possible, that illusion of simplicity quickly breaks down.
Aside, I wonder how long UK dialects will survive: my kids often come out with US Americanisms - of both word choice [garbage] and pronounciation - because of the media they consume.
I do not know much about UK dialects, but someday US will speak a Kiwi-influenced dialect. Received Pronunciation will survive due to preservation efforts.
Look at Czech or Korean. Nothing is 100% perfect but these are pretty close to.
> For example, different dialects can interchange "o" and "a" sounds, how this should be solved in a "proper" phonetic system?
Use å ;-)