SciHub great, it really is something else though. ArXiv does cover a bit more than just math and physics, there is some biology, compsci, finance, and economy. But yeah, would be lovely for it to branch out. But that is probably also related to how the fields functions. If the fields do not have an open preprint process, I can imagine quite a bit have to change first.

It is a preprint site, because that is what the researchers need. It’s a great tool to “publish” inofficial books and lecture notes in addition to actual articles for journals. For the public, I see no issue. You can see it right there on the arxiv if the article is published in a journal or not (unless the authors are sloppy), and, you can go back to earlier revisions, to get a more detailed view of what the referees and editors did not allow to be published (implied by the changes made).