the billionaires have a lot of money as individual anomalies, but most wealth is generated by corporations that must pay market rates for labor or else they will get undercut by other businesses; labor is never cheap. Thus, those at the upper-echelons of the working-class--managers, senior engineers, etc.--as a class, hold the most significant stores of wealth in the US, perhaps far more than all the billionaires put together. I think about 10% of US workers make between $150-$300k a year, so multiply that number by twenty million--something like 2 trillion dollars just in one class alone. Billionaires cannot possibly account for the vast majority of GDP.

Let's not forget that in the last 10 years the US has added approx 12 trillion dollars to its GDP which far outpaces inflation in that same period, meaning absolute wealth in the US has increased remarkably--and, yes, the majority of that wealth is paid out to workers who make up the largest class in the country.