As a person who spent a long while in the community at certain points, anytime it felt like it was "waning" was mainly due to my own slow disinterest in it.

It certainly isn't as huge as it was a decade ago, but nothing before or after was as huge as that, there's a reason it has like 750K stories on ffnet.

As for the state of the fandom, well, I consume a lot of trashy fanfics (see; WBWL). I'll say those have mainly stayed the same in terms of quality over the years, but that's mostly because you'll always have new readers come in, see something they like, and their first story will almost always be fairly poor, as it's a learning experience, and then they'll become the older writer publishing good stories and (hopefully) be around to critique new upstart writers, and so on.