The bulk update request #10262 has been rejected.
Genre tags are inherently nebulous and subject to frequent mistagging. forum #212293, to me, is a signal that they invite more harm than good, even if we were to garden them. Cowboy western was a pain in the butt due to it originally being just western and still has issues with people tagging it based on series canon.
I know this isn't going to be a popular BUR and that I'm definitely missing more genre tags that I plain don't know about, but genre studies are nebulous in and of themselves involving debates that people make their entire doctoral dissertations about. I don't think we need to deal with that on danbooru.
All genre tags are relatively easy to find via other tags, such as cowboy hat and mecha.
...though fantasy is honestly the worst of the lot. There're car pics, Goku, random Genshin characters, topless women... Yeah when this BUR gets rejected I'll probably submit a fantasy-only one.