You are touching upon a lot of interesting aspects concerning genres, categories, hierarchies, etc.
Some of them I have been/am struggling with a bit myself.
I started to write-up a reply trying to address all of it, but I quickly realised it would become a ten-page essay.
Which could be interesting for another thread/topic, but not so much for this one.
So I'll try to curb my response to what pertains most directly to Picard and my system.
I had set up Picard to grab genres by way of the MusicBrainz tags with your previous instructions and all I get is crap, really.
I'm not familiar with that artist, but running that album through Picard for me results in this:
Which to me doesn't seem deserving of the description 'crap'. But then again, I'm not familiar with the artist, nor much with the type of music to be honest.
Looking at the genres you manually applied, genres such as 'Urban Adult Old School' 'Smooth G-funk' are not in any genre database that I am aware of. So indeed, those will not be retrieved.
But as soon as you or somebody else adds these as a tag to the recording @MusicBrainz, they will be instantly available to anyone.
If you are interested to test it: I just added 'New jill swing' to track #1.
If you re-run Picard on it you should now see it showing up.
(you do need to add '+ New jill swing' to the whitelist first)I understand now that (and why) you personally will still not be happy with the result, but if people with expertise on specific music add specific genres such as these to the MusicBrainz database, it will be an improvement for many to benefit from. And it's not much work.
Also it wouldn't be hard for me (or yourself) to add more (sensible and broadly agreed on) genres to the whitelist so from then on they will also get retrieved.
About genres, categories, subgenres etc, I think it's simply impossible to create a strict hierarchy where you can put every piece of music ever produced in one specific box.
Many 'genres' are sometimes categories, sometimes genres, sometimes styles, influences, and sometimes describing a social/political movement and period.
If you wanted to cover those (and some more I could come up with) you will need a lot more tags than just 'genre or 'subgenre'.
And a lot of music just can't be restricted to be placed under a single higher level category.
For one song, Person A would place it under the category Pop, Person B under Rock, another under Electronic, another under Latin, another under Soul, or Folk, etc. etc.
So my perspective on this matter (for now…) is that I just like as much as possible appropriate genre tags attached to a song.
And that is what this Picard system of mine is aiming to do.
For an Elis Regina song, I am fine with ending up with something like: MPB, Bossa nova, Brazilian, Latin.
None of them will pinpoint the song exactly, but they are all 'correct', and the Tag Hierarchy Browser will then allow me to find the music where I would suspect I can find it.
And if I find that somebody labelled it as 'Pop' or 'Vocal jazz' in MusicBrainz' database, I can easily vote it down. And if at least a few people agree, it then will be gone.
So concluding:
My quest and aim is different from yours.
I would like to have all my music getting as much as possible not-incorrect genre tags.
It's easier (for me) to use filters to narrow down a search having such tags available, than not to be able to find music because all more generic (but correct) style or category genre names are absent or removed, and I forgot that I labelled a song as 'Alternative symphonic indie neo-proto synthpunk' ;-)
