Even if he's wrong on that point does it invalidate the basic premise that other businesses suffer at the expense of the companies which are overvalued?
It could. When there is a lot of talk about startups in the press, that increases the supply of programmers, because it makes more people study CS. But as I pointed out in another comment, big companies could be responsible for more of the increased demand for hackers than startups. If so, "overvalued" startups could be net helping rather than hurting the job market.
I'm not saying this is the case. I don't know. If were going to write about this topic, I'd start by looking at the world and seeing what's actually happening.
(at least thats how I read it)