You are deeply misinformed or perhaps intentionally misleading re: your characterization of Marx's ideas. Marx's theories on mental labor appear in his earliest works, and continue through his later, more developed ones:

labour-power or capacity for labour is to be understood the aggregate of those mental and physical capabilities existing in a human being, which he exercises whenever he produces a use-value of any description.

Capital V1, chapter 6 -- where Marx defines labor power

Your characterization of Marx's ideas, that he is creating artificial divisions between different kinds of labor, is in fact a tendency of capitalism that Marx identified and criticized at great length.