I began my writing journey on fanfiction.net after a fan page on wetpaint.com went down (wetpaint was my OG springboard for all things fanfics, then ff.net, livejournal and tumblr). I still visit it from time to time, reading fanfics that are not present on AO3.
What about you? Do you still visit ff?
I stopped crossposting my stuff to ffnet around 2017. A lot of effort for not much return. AO3 is just so much nicer to look at, navigate, and add tags/summaries (boo @ ffnet’s summary character limit). And AO3 allows all the whack stuff I write (explicit, original works, RPF) so it’s pretty much a one-stop shop. I might peek at ffnet if I’m desperate for fic, especially for old shows who had their heyday before AO3, but if I’m that desperate I’m usually writing my own fic at that point.
Oh my. Now I’m intrigued. Haha. But you are so right. Ff.net has so many gems that are just not on AO3. I still crosspost though, if only because I still have some readers there. But I do notice that activity has decreased over the years.