The post briefly flirts with a refutable hypothesis, and then degenerates into a tautology. They start with conditionals - often, they don't contribute well, and "they may become fixated on trivial tasks. This leaves open the possibility that some workaholics are, in fact, focused on the right tasks and contributing well, (though perhaps at the expense of their own health and sanity).

The rest of the post essentially turns often into always, and may into will, and at this point, yeah, it becomes a tautology.

That said, I think PG wrote that a startup is a way of compressing a lifetime of pain into a few years. It probably isn't sustainable for a lifetime, or even a decade.