This concern over income equality needs to have a reality check. I assume that no one wants to live in a society where everyone is equally dirt poor which means income equality is not a problem in itself. It must combined with other statistics before you can say whether the numbers are a concern. Two immediate questions come to mind:
1) How does the US compare to France wrt income growth?
2) How much of the difference is due to rich French people simply leaving the country?
IOW, if *absolute* incomes for the lower 50% grew in the US but fell in France then we don't really care that the *share* of income held by the lower 50% dropped.
Similarly, French policies may discourage wealth accumulation but if that has the side effect of slowing job growth and business creation then that bad for France in the long term.