There is not good evidence that peer review improves quality and there is perhaps some to the contrary (many predatory journals are peer reviewed). The arxiv (unreviewed) is among the most reliable sources available.

I think it's a bit different considering the goal was a teaching tool of well recognised conditions

>all or almost all were cases of very well recognized conditions [...] where a single case report would not generate any interest or ever be cited.

That is an ironic proviso given that the article clearly states

"The peer-reviewed articles don’t state anywhere the cases described are fictional."

Peer review by peers who are trained by non-replicable science is not helpful...

Independently replicated. Reviewed says pretty much nothing.