Gold compared to what Microsoft and many commercial ISVs dump on their customers as "documentation".

The Arch Wiki is superb, indeed. Let's call it platinum. ;-)

My issue is that if volunteer driven projects like FreeBSD, Arch Linux or OpenBSD can provide very high quality documentation, I expect commercial ISVs to provide documentation that is at the very least that good. Instead, documentation is often either missing entirely or very bad. Or they have the audacity to charge you extra for a manual.

Arch wiki is different, imo, than the manual in that it focuses more on individual applications that run on the system whereas the handbook focuses on the system itself. I have used both on freebsd, FWIW.

There only better wiki I have seen is the Gentoo wiki.