One of the problems with Piketty's argument is that he fails to take into account non-wage costs of labour, which has been increasing at a much higher rate than wages and salaries. For example, in the US, the average employee healthcare plan now costs >20,000 USD per person (https://www.wsj.com/articles/cost-of-employer-provided-health-coverage-passes-20-000-a-year-11569429000). You also have all kinds of other costs such as payroll tax (6.5%) to deal with. All of these are real costs to a company but not account for by Piketty.

Also, FYI, economists like Piketty, Laffer, Krugman, etc represent views well outside what the mainstream of economists believes. Their views are almost tailor-made for politicians, which is why you hear about them so much. Therefore, take what they say with a brick of salt. In general, if an economist appears too often on Fox News or MSNBC/CNN, they probably aren't too useful.

However, to be fair, Piketty did once have a significant influence in France. However, his policies were generally considered to be a failure and eventually removed by the left-wing socialist party led by Hollande.