You'd certainly think so. But never underestimate a user's ability to jury-rig a piece of software into doing something it wasn't designed to do, ignoring any and all obviously better solutions as they do so.

I don't think I've ever actually seen documentation published on Discord and nowhere else. But I do very often see no documentation whatsoever except a "just ask around on the Discord" link serving the role.

Discord probably isn't used as a robust ticketing system either; usually if anything it's a bot that will push all tickets to an actual GitWhatever issue, which is fine. But again, what I do see often is projects with no ticketing system whatsoever, and a Discord link to just dump your problems at. If the issue tracker on the repo isn't outright disabled, it's a ghost town of open issues falling on deaf ears.

Announcements can be pretty bad. Devs can get into a habit of thinking the only people who care about periodic updates are already in the Discord server, so they don't update READMEs, wikis, or docs on the repo as often as they should, allowing them to go out of date.

Fwiw I've also seen several projects that have Discord servers with none of these problems, because they handle all those other parts properly.