I can't say that I've ever seen genuine uses like this that you mention unless it's a 'community' for adult content or sketchy content. Is this that common?

Uses for what? Here is Russia many companies have (or had) groups (not Slack or something else but Telegram), most communities exists solely in Telegram, most news channes are also there.

Not to mention you create ANY kind of bot without any trouble.

I guess we just live in two different worlds. Like with China where WeChat is the default. (except we now have fucking Max instead).

It's usually where i get news about custom LineageOS builds for various devices