Your comment is quite far off from reality.
To address your first point: he started the company deliberately. He had sold a successful company before Facebook. He also turned down multi-billion dollar acquisition offers because he knew exactly what he was doing and what the opportunity was. Many of the funding rounds for FB were red hot and everyone was trying to get in.
And to your second point: what he built is unprecedented. And because it is unprecedented, there are a lot of questions that we as a society need to answer collectively about the role a product like Facebook plays in our lives (kinda just like with every other new, transformational technology, including email). But to call his execution "In over his head" is laughable. I don't think other leaders would have fared any better and many could have fared much, much worse.
Now, are there questions and valid criticisms about his execution today or his handling of the recent controversies? Of course! Does that mean he's a random guy with a side-project that accidentally blew up and suddenly he's in over his head? Absolutely not, your comment is more fantasy than reality.