GitHub and Discord are widely considered the best options in their field.

Git, sure, I seldom hear anybody complain about it, and git is literally the host for most FOSS, so supporting it isn't exactly hurting the cause. But suggesting Discord is the best depends on how you're judging that criteria. Best for who? Admins or users?

Moreover, if we're going to start getting into the nitty gritty about what the "best" options are in any field, then FOSS dies in most cases. Volunteers simply cannot compete with a bunch of paid developers, but they will do their best.

Plex, for example, blows Jellyfin out of the water in terms of polish and simplicity. If you're judging best on how easy it is, and how likely it is the average person's going to run into issues, Plex beats its FOSS competition by a mile. But that's not the whole story, is it? That doesn't take the enshitification factor into account, or the fact that forces you to pay for certain things that your computer is effectively doing on its own.

But the other thing to remember is that what truly kills FOSS is people just simply not supporting it. The more you use these established, centralized, biggest names, the further you entrench them, and the harder it becomes for any serious alternative to justify its existence.