While we don't have the Traveler and Proxy umbrella tags for the two other miHoYo games that do have selectable player charas (and recently, dealt with the Byleth umbrella tag for FE), I noticed that no one had thought of applying the same for the Trailblazer without a valid argument.
Evaz's justification for removing the umbrella Byleth tag in forum #337873 applies to the Trailblazer for the most part.
The only reason to have these umbrella tags is so that people can search for both versions at the same time, and because sometimes in rare cases you can't tell if it's the male or female version of the character. But in reality most of the time people are just looking for the female version even when they're searching for the umbrella tag. Cases where the gender is ambiguous can be handled the same way we handle Male/Female Ritsuka from Fate: by taking your best guess based on context, or by tagging both if you truly can't tell.
In the context of HSR:
- "Original purpose was so people can search for both at the same time": miHoYo treats both male and female selectables equally in promotional art, whether it be Genshin, HSR, or Zenless. Having both in the same pic for special occasions (e.g. post #5297060) wouldn't be any different from something like post #9210299, and it reflects in fanart if artists want to. Also, we have a rule that any art portraying Caelus and Stelle together warrants the dual persona tag.
- The case of "rare instances where you can't tell if it's Caelus or Stelle" does have some precedent: the wanted poster in the Belobog arc (post #6269369) was deliberately made ambiguous to allow player-side interpretation as well as removing the need for miHoYo to make separate gender-specific wanted posters. And most arts of that wanted poster are paired with either Caelus or Stelle, easy identification.
- "Most of the time, people just look for Stelle": 8413 > 4674, with Stelle leading in post count. Caelus normally only gets attention if it's a Firefly hetero pair art (or recently, Castorice), as noted by someone on the Discord.
- A unique issue is the Trash Cake cat form, which implies the Trailblazer directly. The easiest way would be to alias it to just "Trash Cake" and deimply it from the Trailblazer umbrella tag.
- Just like Byleth, Caelus and Stelle have their own costume tags already implicated to themselves and not to the umbrella tag, making it easier for us since we wouldn't need to touch those unlike in FE.
Long story short, the Trailblazer umbrella tag can be taken care of since there's enough arguments and prior precedent to do so. Not to mention we wouldn't have issues for such a move (barring the Trash Cake bit). I'm leaving this to others to cast opinions before any BUR.