@AbyssalMonkey
Vampires, zombies and ghosts are cultural phenoms but are they relevant in manga cultures? Frankly, I don't know either but if you ask me which shows up in mangas more as a main or sub theme then I'd go for tomboys, unless you count every fantasy with zombies and ghosts as monsters in them. Then wouldn't tomboys be more of a content tag?
I don't really think it should be a content tag but I also don't think that just dismissing it as a fetish tag is appropriate, great examples of this would be Tomo-chan wa Onna no ko! and Biyaku Cafe where being boyish is actually the main theme that the story revolves around. The point is there are niche genres in media are actually quite common in the manga culture.
So here's my take on this, MD shouldn't only have content and containment tags, rather also have tags that are actually popular and relevant in the manga culture, I'll call these "compound tags" for now. These compound tags are usually in between two other genres. It's kinda like colours where if you mix main colours you get a compound colour BUT these compound colours are also widely used, right now that's what it feels like Tomboys and other tags like Villainess/Otome where they're in between two genres but are also popular in and of itself. This is why I actually think gyaru is a valid tag, I do think it was created far too early especially when we have a delinquent tag.
I do heavily agree you with the creation of a guideline. In the end MD will have to make a choice and create a tagging guideline, and they need to do so quickly. Only time will tell whether people will have to use another website in order to find series with these kinds of tags.
Edit ---> I was actually thinking about primary and secondary colours but got too into the word "compound"🤣