What's wrong with your overall summation of the situation is that the housing crisis is -- like most things that go systemically wrong in economics and public policy -- a product of multiple sources of causation, acting in concert.

That's why you can't (meaningfully) just say, "See, there's this other favor X [lack of middle class salary increases] at play. Therefore this factor Y everyone keeps talking about [high-salaried tech workers pouring into town] can't be the major factor. In fact, it's merely trendy."

Because in reality the housing crisis is a product of X, Y, Z, and a host of other factors acting in concert.