I use Arch Linux and FreeBSD quite a lot and I agree that the Arch Wiki is great but it's not really comparable to the FreeBSD handbook.
The handbook feels... like a proper handbook. It's got structure and is very comprehensive. The first time I installed a non-Windows OS was FreeBSD as a teenager using only the handbook (I had no internet connection). In hindsight it was an amazing learning experience.
The Arch wiki is more like a compendium of arcane knowledge regarding Arch Linux and a lot of Linux software. It's a lot broader in scope but it can be a bit overwhelming when you don't know exactly what you're looking for.
Compare for instance the entry for OpenSSH in the handbook vs. the Arch wiki:
https://www.freebsd.org/doc/handbook/openssh.html
https://wiki.archlinux.org/index.php/OpenSSH
The FreeBSD page is a lot shorter but it's also more beginner friendly IMO. It ignores the more advanced features and niche use cases to get the user started. If you want to go deeper than that you're supposed to go look for the full documentations elsewhere (man pages, info pages or... the Arch Wiki for instance). It's short and focused. The Arch Wiki page on the other hand tackles many other advanced features of OpenSSH but I fear that a complete beginner might find it a bit overwhelming.
The Arch Wiki is priceless though, it's become my de-facto resource for projects that don't offer good quality first party documentation.