I am not sure how I could attract followers if I didn't have a place to publicly exhibit my wears.
At the moment the main socials like Twitter, Facebook and Instagram, give each person an opportunity to share randomly. To broadcast would be a better word I think.
I am not sure how you could do that without the proprietary platforms.
Connecting with those I already know can happen without the platforms as you said.
I may be missing something. For the moment, as far as I can see, the ability to do something doesn't equate with the ease of doing something.
We can connect without the platforms, but the platforms make it easier.
For example, I would never have read your writing without Medium, which is just another social media platform. You broadcasting such that I see your content without this platform would have been much more difficult, and probably have reached a smaller audience.