I agree with the GP; my view is that virtually all 20th/21st century philosophers dug up classical German/Western philosophy from its grave and made their careers out of it. That philosophy had nowhere to go, so its adherents could take it anywhere in the service of their -- to be frank -- grifting. All it takes is a clever tongue capable of generating "fashionable nonsense" and a lack of intellectual integrity (see: Sokal hoax).

Ludwig Feuerbach and the End of Classical German Philosophy (1886) by Friedrich Engels, published after the death of Karl Marx, is one of the best summaries of the late development of classical German philosophy in particular. It's written in a fairly accessible style as long as you grok the Hegelian/Marxist idealist/materialist definitions.

This revolution in Western thought is best summarized by Marx in his final Thesis on Feuerbach (1845): "Philosophers have hitherto only interpreted the world in various ways; the point is to change it."

The upshot is that the best way to understand writers/philosophers like McLuhan is rather to understand their audience. Which bits of "fashionable nonsense" is sticking, and how does this reflect the conditions and interests of the audience? Presume market forces before presuming intellectual rigor.