Take, for example, the statement "America is richer than Mexico." By which is meant, "on average, Americans are richer than Mexicans." Someone else could say: "But there are plenty of homeless people in America, and Carlos Slim is the richest man in the world! There are vastly greater internal differences in wealth within America and Mexico than the difference between the two countries' averages."
Perfectly true. But, it doesn't then logically follow that America and Mexico must not differ in terms of average wealth, or that the difference in average wealth between the two countries is irrelevant or less relevant than their internal inequality.