So I have to ask, why use Slack for hobby things instead of Discord? Is that driven by people used to having it at work? I'm confused by the thought of "hobby Slack channels".
What do you mean? The analogue to rooms would be channels, which falls under a server.
It seems to me that the main organization model of Slack and Discord are the same.
What about any of that is embarrassing or childish? That it's not specifically designed for corporate drudgery hell?