I'm using MusicBrainz' Picard and some tweaked plugins and scripts to retrieve and write genres.
I have set it to write a maximum of 20 genres.
But in reality, on average it will result in something between 2 and 6 genres being assigned.
It resulting in more than 10 is very rare.
I would delete the ones I find to be completely wrong or useless, but the results are pretty good actually, and I am not convinced it's worth my time and effort to do a lot of manual editing.
And when I feel compelled to do so, I don't edit my files, but I edit the release at MusicBrainz.
So at a next synkgronization my files get updated accordingly. (and hopefully other MusicBrainz/Picard/MusicBee users also benefit)
And, as a full disclosure: I am not allowing any software to touch/write/edit my 'genre' tag.
I have a custom tag 'genre retrieved' that gets populated like this.