I have not even started to read Thomas Piketty's Capital in the Twenty-First Century, but I have heard of Piketty as compared to Marx.
Whatever else Marx was, he was a very learned man. He read the works of virtually all political economists who came before him. And in his lengthy tomes, he would comment on them, not always fairly. He did not confine himself to ones that were politically influential among the elite. For example, consider Marx on the Ricardian socialists.
So if Piketty is like Marx, can I expect to find comments on the Cambridge equation, r = g/sc? Can I expect to find something about the models of growth and distribution put forward by Richard Kahn, Nicholas Kaldor, Luigi Pasinetti, and Joan Robinson? (Joshua Gans has also noticed a parallelism between the work of Piketty and the Post Keynesian theory of distribution.) Or maybe the analogy is not complete.