This is an issue that takes a toll on my efforts to ‘get genres right’ too.
Very glad I’m not the only one losing sleep over this 
What player is that?
I’m mainly using Jellyfin ATM. Gelli on android. I also have a Navidrome instance running cause it’s very fast and light weight. I got tired of desktop music player if I’m being honest.
B.t.w. I don’t think Steampunk is a genre. Maybe a style, or maybe a keyword/description.
For the Steampunk “genre”, yeah it’s mostly a style, and I must admit, although I love music I’m not too “geek” about it (in the sense that I don’t know much). I love tagging that as it makes it easier to find similar songs/albums in my library, mainly because when you self-host you don’t have the power of machine-learning and human curated playlists from what other people listened/are listening to like Spotify have for example. Having more “genre” makes it also easier to make smart playlists 
(once Jellyfin implement those)
If you care to share such a list, although I agree with you it is subjective, it would make my life so much easier than trying to compile one from scratch. I’m planning on copying the “approved” list of genre from MB and add what it might be spelled like to it can be unified. (Making sure both upper case and spaces are ok)
I do visit last.fm to get some inspiration of “style/genre” on some albums I find lacking in tags (tags here refer to the list of genres), again to make it easier to find.
On the side, also regarding genre/style:
My main frustration is coming from MB where you can tag artists, release group, album and specific song, but no way to easily edit those.
For example, I saw a 06 tag on multiple songs from 1 specific release.
I also had to copy multiple genres from an artist to like 20 release groups so Picard would use them. And then go through all the releases because someone tagged Punk on a hip hop artist that doesn’t do punk at all - although this might also be subjective but the consensus across multiple sources was hip hop/trap/emo rap.