This is straight up denialist and hyperbolic FUD. There's a healthy and vibrant ecosystem surrounding the federated social web, which has been a thing since 2008 or so.
Also, I would argue that email's staying power isn't quite backed by the answer you gave ("it locked everyone in with its network effect") but more along the lines that it survived the Lindy effect (the great thing about this is that it's not going to its grave as a technology anytime soon).
