The only reason I suggest advanced users is due to the fact that the MusicBrainz GUI is not particularly friendly or intutive and naive users might be more likely to damage a track or accidently delete it while trying to edit it. My computer experience IS reliavent as given it is not properly working, it could be contributing to behavior not present in other properly working Mac’s.
MusicBrainz helps users avoid ‘tricks’ and allows them to add additional metadata about their tracks, especially if they are not purchased from the Music Store. It is also useful when recovering tracks with corrupted metadata. That said a well written and properly thought out and tested App should not requre the user to resort to 'trick’s to get their desired results as Music sometimes does. It seems to get particularly dicey when trying to create compilations.
I agree with you about Apple Support. It seems to be a crapshot. Sometimes you get a really good, experienced and well trained agent and sometimes quite the opposite. That is why it is generally a good idea to do some research and get information from multiple sources including the ones you have mentioned.