I have found https://wiki.archlinux.org/, the Arch Linux Wiki to be the most useful single source of information taht is generalized enough to apply to most other distributions.
As an early adopter of Linux, I too found the existing documentation appalling and started writing better documentation, which led to co-authoring RedHat/Fedora Unleashed with Bill Ball.
My advice is to contribute to the documentation yourself since it appears that no one else, including the software authors, care much about it.
But the barriers to contributing are high. You may not only need to learn about the application, but you need to learn any number of arcane editing and versioning tools, and then convince someone in authority to accept and include your changes. It's really no different that contributing code to a project and for your average writer, that's a huge hassle and likely a big part of why more writers don;t contribute.