You described almost exactly what I was thinking while reading this article. It's not so much that "the old internet" is dying but more that a larger mainstream audience is using it. In the past the internet was mostly used by a younger and/or niche user base and seen as abnormal by most people. Now that more and more people have smartphones, laptops and PCs with access to the internet, the user base has become more homogenized. It is no big surprise that content seems to be stream lined and made bite-sized.
I don't necessarily see this as a bad thing, as I believe that there is still a large user base searching out beyond the social media hubs. We see the users of sites like reddit (and hubski) constantly looking for and sharing content from across the web. This content may be random, dumb cat photos or a long form blog taking a philosophical look at the evolution of the internet.
It does seem upsetting that a majority of users will ignore most of the internet and only use social media but I don't think that a lot of them would be using an internet without social media. When you take a look at the evolution of the internet you also need to look at the growing user base and what's attracting them.