If you divide the GDP by the number of employed people (including self-employed and entrepreneurs), you get a bit over $180k/person. The median full-time income is a bit over $60k. In other words, as a gross simplification, the mean worker earns 80% more than the median worker.
The comparable numbers for Germany are a ~€100k, ~€45k, and 35%. If something is hollowing out the American middle class, it might be the high earners rather than the capital.
