1. Marx on Hegalian Dialectic-This was not central to G.W. F. Hegel's aesthetic writings. Hegel used it in his logical discourse, as it appeared natural in nature, however, it was not created to "control" or manipulate others.
2. Immanuel Kant-Rand claimed Kant was the "most evil man in history". One, that is false, simply because, well...I take that claim. Secondly, Kant's "Critique of of Pure Reason", or his "Prolegomena to Any Future Metaphysics", simply demonstrated how man is able to formulate and synthesize concepts in space and time, governed by certain universal laws or principles. He was NOT attempting to usurp reason. Not at all. His treatise simply acted as a guide to "tighten up" or strengthen the process of our use of reason. It is a disservice to all scholars to accept this Argumentum ad Hominem pushed forward by Rand, and never investigate Kant's work on this subject. Many may take issue with Kant's analysis on Ethics, as that is quite fine.
3. Marx on Labor Theory of Value-Marx believed that Labor spawned the end value of a product. When a firm sold that product, the "profit" yielded was not "shared" with the workers. This is a false hood. The notion of value is subjective to the individual, as we have preferences of things we act upon. The work of Eugen Bohm Bawerk debunked this labor theory of value, in his work, "Marx and the Close of His System". It is a devastating blow to Marx's work in "Das Kapital"..
Ayn Rand has a cult-like following, as does Karl Marx. These incidents of bad scholarship does not mean that their overall work does not have any meaning, or make them less relevant. It just means that the Kant and Hegel deserve deeper investigation. Also, the notion of the labor theory of value requires deeper critical epistemological analysis.