[throwaway91111]

What are you imagining the hayday of email to have been like? It sounds like you're describing AIM in the 90s, or SMS in the early 00's. Before that there was IRC if you wanted realtime responses. Email has always been async.

Mind you, nobody has ever introduced me to a friend via social media.

Meanwhile, SMS is still going strong. Who needs an app?

[scbrg]

There are several advantages of apps over SMS. Cost and accessing the messages from multiple devices being the two main ones I can think of.