We develop and calibrate an analytical growth model in the Post-Keynesian tradition with an endogenous wealth distribution and differential returns to wealth between workers and capitalists. We show that a long-run equilibrium allows for non-zero wealth owned by workers, even as the model contains the "triumph of the rentier" predicted by Piketty as a special case. The model's calibration to ten European countries shows that the distribution of wealth is likely to become more unequal in all cases, barring political countermeasures.