What you think of as “the classical theories about capitalism” are after-the-fact rationalizations which reflect neither the motivation for the development of capitalism (class struggle between the mercantile class and the feudal aristocracy) nor its actual operation in the real world, and which were developed defensively in response to the original (and critical) theory about capitalism-as-an-existing-system, which absolutely does not cease to hold in the presence of monopoly, or view the emergence and maintenance of such a condition as aberrant.
