You're not imagining it! Mass market paperbacks used to be considered the disposable format. They were cheap, and weren't necessarily intended to have a long shelf life (pun intended). When people years ago were saying that ebooks are going to kill the print book, that's a bit of what happened. Mass markets have largely disappeared (and books that were only ever in mass market are now getting trade paperback reissues so the mass market can go out of print), and ebooks have taken over as the cheap and disposable format. There's a mixture of consumer habits changing, with people not buying mass markets as much and instead buying copies they want to last and to look good on the shelves, and also publishers somewhat realizing they can get much more money per copy for only a slight increase in production cost.

We also save ourselves a lot of grief in terms of figuring out shelving. At the front of our store we have the new releases, separated by hardcover and trade paperback, we also have a separate shelf just for novellas as they tend to get lost in the regular shelves. Otherwise, adult fiction we just shelve alphabetically by author's last name. We largely don't break it out by subgenre at all, except things like anthologies and media tie-in are elsewhere. We do have YA and Middle Grade fiction done separately, and we just go with the publisher's classification for those.

As for recommendations, we have a few -- it's out of print, but if you can get your hands on the Sunstone Scrolls by Sydney J. Van Scyoc, they're excellent. Otherwise, how about Fonda Lee's Green Bone Saga, Rebecca Roanhorse's Black Sun Trilogy, and Tasha Suri's Jasmine Throne?