I think you're redefining "social media" (which I think was previously called "social networking" once upon a time) as "broadcasting" and "megaphones" so naturally your definition doesn't fit.
But socializing online is about sharing information, interests, and building a (small, or the size you prefer) network of people you consider online friends.
Discord does seem to work well for chatting about those same things with the people I know, and I can easily see how others use it for the same usage but with online-only friends. But whenever I visit my corner of the fediverse, I see lots of like-minded people sharing content that's relevant to me (the hashtags I follow), and I've engaged and enjoyed the experience.
There was and is no reason why any of that requires "large scale commercial and entertainment activity", and, in fact, those things seem antithetical to building up a community of people you want to communicate with online about your interests.
I still prefer when the world was divided in forums, not friend groups.