One cannot simply pay more on average. The demand for good engineers is high and Facebook must compete for them. I believe supply and demand with market rates

One cannot simply pay more on average. The demand for good engineers is high and Facebook must compete for them. I believe supply and demand with market rates is a much bigger factor on the average Facebook engineer salary than the quality of the engineer. For one, we are only dealing with a discrepancy on the order of 40-50%. Is a good engineer only 40-50% better than an average engineer?