I am curious about this. Isn't it the case that most interesting new articles are available on ArXiv or one of the newer preprint repositories that seem now to pop up every day (often with funny names such as engrXiv or Frenxiv)?

Did people really stopped reading arXiv, like they stopped reading journals, and moved on to Sci-Hub completely?

Or the final published versions are substantially different from preprint versions often enough to make Sci-Hub is so important?