What it comes down to is that paywalled documentation is, in my experience, universally inferior to documentation that is publicly available. In my last job I saw "Proprietary Information of <company>" stamped over all the documentation I used, and the thing was the most insulting thing I'd ever seen. The "information" was less useful than the reverse engineering my colleagues had done over the years.

Red Hat's documentation is better now, but documentation tends to rot when people can't see it until they're in the midst of using it. I feel entitled to the knowledge base because I'm not paying for something unless I have a good idea of the sort of issues I'll have when using it, and what the company does to resolve them. Red Hat has made a fine business respecting this up until now.

On the other hand, a lack of publicly available documentation is less important when source is available.