The release of fate/grand order resulted in the massive expansion of the fate_(series) community. Many of the fans who are spearheading the popularity gain were introduced to the nasuverse through the phone game. And through the phone game, these new fans have branched out towards the other installments in the franchise acknowledging that they already know who the servants are. This is the reason why fate/apocrypha has a larger viewing audience than fate/zero or fate/stay night even though it's generally considered the worst out of the three.
At this point in time, the notion of using only class names as tags is causing confusion for the database. The original purpose of using class names instead of true names is rendered pointless, sometimes not even because of Grand Order. In stay night, we are instantly told who assassin, lancer, berserker, and true assassin are. In Zero, we are instantly told the identities of every servant except for Berserker. In Extella, we know who every servant is as it spoils the true names for every servant in EXTRA, stay night, Zero, and Apocrypha. Every subsequent installment in this franchise has the expectation that the audience already knows any previous installment's servants' true names and the stories they were involved in. Yes, the creators' treatment of the audience may not be something that you like, but it is what is happening. Spoilers—specifically those related to true names—don't matter anymore and, in some cases, have never mattered.
Also, the idea that danbooru protects spoilers at all costs is rather silly. For instance: "I am your father" from star wars. post #2252943 and post #2761941 both feature the most spoilerific moment in that franchise's history, but neither post has the spoiler tag on it. Looking up star_wars spoilers will give you posts related to star wars: the force awakens and rogue one: a star wars story; there are actually a few images which I'm rather confused about why they were tagged with spoilers, but whatever I guess. On a similar note, pool #11684, due to its very nature is filled with spoilers about the fate (series), but none of these posts have that tag.
I think it's time to just have the tags as servant_name_(class)_(fate). Tags like demon archer, sakura saber, saber alter, lancer_(fate/whatever) are only causing confusion at this point. In Grand Order, Nasu has redefined what the purpose of the Grail system is, effectively abandoning an old archaic system that wouldn't serve their story right, and it's about time we do the same. We should have something along the lines of artoria pendragon santa alter (rider) (fate).