Even if that was a falsifiable premise, that's not a very strong argument. If "average" income goes up just because there are a few more billionaires that move

Even if that was a falsifiable premise, that's not a very strong argument. If "average" income goes up just because there are a few more billionaires that move to my city, it doesn't actually mean I am richer. If most people are living measurably worse lives because of crime, but the already low rate of murders drops a few points, I don't think we should rest on our laurels.