I do this for my open-source self-hosted project. The reality is that Discord provides a good experience, with good controls for a community, in a way that's friendly and easy to access for many. Additionally it saves me the hassle of hosting something.
I don't see it that differently to using GitHub for hosting the code. In terms of privacy at least it's fairly clear to users, wanting to chat, that their data and content will be owned by discord. Users have the choice to enter the chat or not, it's not required to browse the website or use the software.
I get what you're saying, but since Discord is often used for technical/community support, it probably is a low-friction way for people new to the homeserver stuff to get help and learn more. I know many of my normie friends would never use IRC, even if it was E2E encrypted and kept no logs.
My experience with Discord is that I hate to search for past content on it. I had to do it a couple of times because Google / Stackoverflow didn't return anything but burying the solution to a problem in a chat doesn't look good. IRC had the same problem. For some reason Slack is a bit better at it, maybe because I only use Slack for customers' projects so I know what to expect.
Discord search is a terrible piece of shit, I agree. The real value is the realtime support offered. It should never be a knowledge storage, that's a job for a wiki.
Does chatting on a discord somehow push all your local cloud photos and files to the internet? No? Yeah, its not a big deal. Discord is by far the best chat tool today.
I don't see it that differently to using GitHub for hosting the code. In terms of privacy at least it's fairly clear to users, wanting to chat, that their data and content will be owned by discord. Users have the choice to enter the chat or not, it's not required to browse the website or use the software.