I've started using PWA's intensively via the edge development version. I have to say, for many purposes it's as good, or even better than an app. Even if the website is not an actual PWA.
For social media, it's a perfect fit. I've still been using apps however for any form of messenging (messenger, skype, whatsapp), which thankfully have UWPs. At least, no one has designed a PWA messenger app yet that 'feels good'. FB's might be close.
And obviously anything heavyweight is better PWA/win32.
Anyway, I can see a real truth to this notion of PWA's replacing the need for most light apps, especially smartphone apps. Indeed, I could see a OS platform running mostly on PWA as a core app platform.