I agree with Philip's comments: most of the core pieces are there, and occasionally something from modern GUI style is missing. Mostly then I've gone without as I built https://github.com/benknoble/frosthaven-manager.
Thank you, Philip, for reminding me that https://racket.discourse.group/t/scrolling-racket-gui-panels-with-the-mouse/957/3 really needs some TLC; this has probably become my number one racket/gui peeve.
My second is also the docs: as we wrote in our paper, racket/gui is a white-box (transparent) framework that typically requires deep understanding of its inner workings (and the racket/class library) to use. Documentation can help this: more examples that are not DrRacket-sized (and that don't come with DrRacket's specific challenges) would be a great help. The same goes for Framework.
In the meantime, if you can do what you want performantly with racket/gui/easy, I encourage you to try it—it's a black-box framework in that components are opaque. This makes it easier to learn and use. The hooks that it offers into racket/gui guts have, in addition to being extremely valuable for complex programs, tempted me to learn bits and pieces of racket/gui in more depth.