I think people are getting too hung up on comparing this to Kantai Collection or Touhou. Azur Lane is a gacha game. Fate/Grand Order is a gacha game. It's not a fair comparison to say "oh, we don't tag outfits for Touhou or Kancolle, so we shouldn't do it for other games". Gacha games today go much further with having dozens of alternate skins/outfits/whatever than past games ever did. Our tagging has to adapt to that.
Once again, I point out that we have literally hundreds of tags for Overwatch and League of Legends skins and it's not a problem. Look at characters like D.Va or Ahri and imagine how you would find their skins using gentags. Nuking these tags would make searching infinitely harder.
I think it's completely backwards that we spend 30 or 40 tags describing every detail of a character's appearance, but then balk at adding 1 tag for the character design as a whole. Distinctive character designs are more interesting and useful to search for than the buttons on someone's shirt, or the color of someone's socks.
Even Pixiv tags Azur Lane skins. That's part of the motivation for this. It's a problem when it's easier to search for something on Pixiv than it is on Danbooru.
And I'm not interested in splitting hairs over what is considered to be a separate character by the game's lore and what isn't. I'm interested in what's useful for searching. Is Verniy a separate character from Hibiki, or is she just Hibiki with a white hat? It's beside the point - Verniy is a popular alternate version, and that makes it useful enough to have a tag for her.