Yes Medium has become a social network of writers. This interaction did exist on blogs but we let the community fall or apart. That or we did not cultivate community as the rise of branding versus blogging became the dominant force.
You can still do this through blogging, RSS, and open annotation (I do) but the network effect matters. I get such little interactions on my blogs. Most of the discussion is on Twitter, G+ (before it died). What medium has done is unite the network and the writing platform.