They (we?) do/did go to school you know... Replace internet with tv and your argument goes through just as well, which is to say, not at all.
The internet is interactive. This easily allows the internet to become a much larger part of someone's life than TV could.
This is a big enough difference between TV and internet that I don't think you can really use TV as a refutation of his argument about internet.
If in practice you accept that other people exist, then you should also recognize that their experiences are probably going to be different from your own.
I've never encountered this issue of expecting this cool person based on a manufactured illusion and then finding them to be mundane. And I know without the internet I might have more of a sense of community in general but I don't think I would have found people as unique and weirdly on my wavelength.
The moment you try to break out of your internet and go meet new people, it frustrates the hell out of you that life isn't as cool and people aren't as witty as they are on internet.
And you start thinking maybe you aren't with right people, so you try to meet the cool people from internet in real-life and it's again same. The same people you enjoy on internet, you can't tolerate them for even an hour in person.
What internet portrays is only a part about a person (which they've edited then edited and then edited again).
What we assume life is like a Hollywood movie and yes retakes frustrate the hell out of us but life is actually the retakes.