I am aware I have died on this hill before but people who really strenuously argue that fanfic isn't "real writing" drive me insane. what do you meeeaaaaannn. besides the fact that any attempt to define "real art" vs "fake art" is inherently reactionary, it just doesn't make any sense. it's Writing. people Write it. what the fuck are you talking about.
"it's totally self-indulgent with no standards for quality and criticism is borderline not allowed"
are you like. aware of the concept of hobbies? if someone regularly posted pictures of their hobbyist knitting projects on their blog, it would be considered rude to drop in with "criticism." that's still a real art form.
"most of it is really bad"
I cannot stress enough how much perceived quality is not a valid metric for determining what is and isn't art
"it's just porn"
I'm going to kill you
"it's full of unchecked misogyny, racism, queerphobia, etc"
I have some really bad news about every artistic medium ever
"you didn't put in the work of making your own world/characters, you just copied someone else's"
tv shows with writers' rooms. ghost writers. franchises where different works are written by different people. adaptations and retellings. sorry guys I guess none of these are real writing anymore.
There is an endemic problem in spinoff novels or cross-media properties like comics, where you'll get a very talented author recruited whose work is generally excellent, and everyone's excited, but then it turns out they don't know how to write fanfiction.
And the result is that the spinoff is really bad. Because the author completely fails to capture the vocal cadence or behavior or motivations of someone else's characters, the narrative tone of the series...they try too hard to the point of making in-universe references feel stilted and unnatural, or do WAY too much exposition about things that shouldn't need to be explained at this level of barrier-of-entry.
The ability to be a chameleon, to figure out and match the "feel" of characters and a world you didn't create, is a learned skill.