@AbyssalMonkey
Funny you mention that, because that's exactly what tags on MD currently are. User Generated. They have groups of people arbitrarily assign tags, the people who upload. So you are going to trust those people, who once upload, never change tags? Seems user generated to me. Also funny you say they're twice as useless, because EH Galleries, a website that uses user generated tags, is basically the gold standard for how to tag. If you've ever used VNDB, they also use user tags. I guess this makes your opinion twice as bad?
Oh,and, I'm throwing my own hat in the ring here, I find the tags here on MD grossly unused and misplaced. Historical and Fantasy may as well be interchangeable. Good luck finding something that is actually based on actual history and doesn't just cover the broad idea of "oh, they've got swords, but not magic, so it's definitely historical" which may as well include half of the actual fantasy created. So for me, this suggestion you have is three strikes, and out.