of course there is no causal relation between website quality and VPN quality. but there is definitely a statistical relationship. setting up a secure and fast VPN is very complex and it's hard to see why somebody would then neglect the entry point to that service. actually I'd assume that this negligence would be likely when the VPN is actually only supposed to serve as a malicious MIM. hence I accept this as a valid heuristic.

There are so many bad websites for good projects. Case in point: OpenBSD and OpenSSH websites looks like ugly colored plain HTML from the 90s but they are still killer projects.

You may be right but I think his own website is poorly designed too: he says that "Private Internet Access" is too long because forced him to modify his CSS, and as a "forum" (link at the bottom of the page) he uses GitHub's issue tracker.