alias dangerous_beast -> mash_kyrielight_(dangerous_beast)

It doesn't matter if it worked fine before. If most users want to search for these tags then the tags have to stay.
Tagging does not exist in a bubble separated from searching - in fact, searching is the most important function in the site, because without it our database and tags become useless. If thousands of users find it intuitive to search for character tags rather than combination tags, then that's what we have to use. And can you blame them? A gentag combination will never be equivalent to a character tag when certain characters have multiple or even dozen different skins, all different from each other and all possibly conflicting in the case of gentags.
See artoria_pendragon_(all) swimsuit -artoria_pendragon_(swimsuit_ruler)_(fate) -mysterious_heroine_xx_(fate) -artoria_pendragon_(alter_swimsuit_rider)_(fate) for example. Imagine if we didn't have the skin tags - it'd be impossible to search for any specific design.
Other tags like bb_(swimsuit_mooncancer)_(fate) in fact have this problem, where there's three different designs under the same tag and you can't search for a specific one without adding two or three gentags. That's the farthest from user-friendly.

NNescio said:

The swimsuits, the cocktail dresses, some of the formal wear, sportwear...

But principally the swimsuits because the others might be inconsistently tagged while swimsuits should always be tagged swimsuits (barring dumb naming conventions like calling something that isn't a swimsuit a "swimsuit" like Artoria's).

If that were actually true, sure

However, what about all these posts that aren't tagged swimsuit, because the uploader either forgot, or just didn't recognize it as a swimsuit(people mistake them for bras and panties all the time, you know), or the character is clearly wearing the skin but the swimsuit isn't actually visible, such as them not actually wearing it.

And then on the opposite end of the spectrum, what about all the posts that are tagged swimsuit but aren't actually the costume you're looking for, because a different character is wearing a swimsuit, or it's just a generic nondescript swimsuit, or hell it's a different skin entirely that just so happens to also feature a swimsuit.

I dunno if you've noticed, but none of these altskins are just swimsuits. They feature a myriad of other details that make up the whole piece. They're recognizable even if the swimsuit itself is missing.

It's almost like... general tags are extremely unreliable and any argument of, "well they should be tagged" is idealistic and not representative of reality.

nonamethanks said:

Other tags like bb_(swimsuit_mooncancer)_(fate) in fact have this problem, where there's three different designs under the same tag and you can't search for a specific one without adding two or three gentags. That's the farthest from user-friendly.

Yeah this is a fate/specific problem with its particular way of treating "alternate versions" and "costumes" and "alternate versions with costumes" and "alternate versions that are pretty much costumes" that makes it a real pain to tag properly. I do think most Fate users who look for Swimsuit BB (for example) know exactly what to expect in the search results though, but it's true that you can't really filter between the different forms unless you add gentags.