[crayola]

Yes the maths are likely right, but that does mean Taleb is being fair to Piketty.

Economics is not just about the maths, it's about whether the maths being proposed (i.e. the model) are the right tool to understand and explain the observed data (and do predictions / counterfactuals). So the question of interest (is Piketty right or wrong) is not a question of someone's "maths" (either Piketty's or Taleb) being "right" or "wrong". Sorry if you find this obvious -- perhaps I missed the point of your question?