Contrary to your descriptions of the requirements for a 21st century economy vs. earlier ones, in think mobility between career fields is probably greater in 21st century mixed economies than the 19th century capitalist ones that Marx was writing about, and that that is in no small part due to the ways in which modern mixed economies adopt elements of socialism and depart from the 19th Century system for which the term “capitalism” was coined.

That is, I think experience has shown that Marx’s description was correct at least as to the direction of effect of the politico-economic system, though probably hyperbolic about the degree of practical freedom from path-dependent career constraints attainable in even the ideal situation.