I think fanfiction as a medium is different enough from mainstream literature in the tools it offers writers that it's a shame that it's not talked about more often. And it's not me saying "fanfic is better than books xD" because that sort of mindset is a symptom of people who aren't particularly well read in either medium. I'm just speaking of like... The little things you get to do with a fanfic that you genuinely can't really do in an original story.
I had a big fanfic in a previous fandom where one of the big reveals was the involvement of a kind of infamous villain, whose presence was built up to and foreshadowed through the whole fic until his reveal without ever mentioning his name, so that the name drop would be a gut punch. It worked especially well because of who the villain was and his presence in that fandom space specifically (it's very complicated) and if it was an original story this reveal wouldn't work at all the way it was written in the fic. Because if you don't have a predisposition to think about that character and his relationship to the hero in a very specific way, then just seeing their name won't do much to you; the reveal and the recontextualisation it pushes upon you hinges on your previous knowledge of the source material.
I think it's an interesting tool fanfic authors are given. One of my favorite fanfic of all time is partially a re-imagining of its source material's canon, and something it does is introduce antagonists much earlier in the story or deepen npcs' stories. It then works to evoke a tragic irony that again wouldn't work if you didn't know the source material, and it's something the author obviously has a lot of fun with.
You could call it cheap or a crutch and I mean, yeah, sure, it is a little bit: the fanfic relies on previously established emotional bonds and stakes to achieve its goal, and in some cases it saves the author from having to 'properly' build up its stakes. But I think it's INTERESTING that it has that tool at its disposal. I think it's a fun thing to play with and I think these built in expectations and emotional bonds are especially why I find story driven aus in particular to be fascinating in the amount of ways you can play with them. You know??
