It's not that rare anymore. And while it's true that there's a ton of low-quality evidence for non-celiac gluten sensitivity, I think it's become clear that there's something important there (and more research is needed, as if that needed saying).

Non-celiac gluten sensitivity is not believed to be fictional-- rather, experts disagree about the details of what it is, how it works, how it is identified, how we should classify different presentations, etc. So yes, the science is shaky, but there is plenty of evidence that it's "a thing"... or "some things".