You can keep tagging files ~forever and still not have them perfect… I just stop after when I think it’s good enough and I might start tagging them again at another time.
QFT!!
My current genre process is more hands-on but it's working for me. When I grab something, usually a complete discography, I look up the artist on Discogs, and use their genre pick. Sometimes I will put in specific genres for specific albums but usually, one genre for the whole discography is good enough.
Normally I can tolerate the Discogs genre picks, and this gives me a pretty consistent and bounded list of genres used in my library.
But like you said, it can never be perfect. Organizing my library can be kind of soothing though, like playing solitaire.
I have discovered so much great new music via Twitch, but I am sure not every genre is well supplied with good DJs.