The question of Marx's ideal of man is quite simple: the whole image he lays forth in his works is overly childish, voluntaristic and outright untenable.
Human knowledge has grown so immensely since the Antiquity, so that the very basic jobs require quite a significant learning period. One cannot simply become an engineer or an analyst, even with a background in the adjacent fields.
James Lindsay and his New Disourses project is interesting in its critique of the Left indeed. However, I believe there is a huge mistake which undermines Lindsay's productiveness as a philosopher: he clings to the Leftism as Gnosticism idea (developing some of the Eric Voeglin's insights) while missing the meta-physical side of the questions.
Religions are not just sets of beliefs. They are philosophies, they have metaphysics – each has one of its own (leave aside the fact that the metaphysics of a religion may change under the institutional pressure – see the Catholic church as an example).
Thus, equating the leftism (or any version of Post-Modernism) with Gnosticism is a huge miss.
There is a certain meta-physical background which may be shared by most of the Gnostics and most of the Leftists. But this is an example of the convergent evolution of the ideas.