[*]The wealthy benefit the most from that flourishing society.
Such a claim involves a lot of value judgements. If you go strictly by net worth this may be true. But alternatively, look at many past societies (and many societies around the world now). One, again invoking some value judgements, could argue the other way.
Let's look at feudal lords and serfs for an example. Feudal lords had wealth and tremendous political power over serfs. Serfs had nothing compared to what the poor (and middle classes which largely didn't exist in those situations) have now. They didn't have social safety nets, laws designed to protect their labor compensation and safety on the job or anything of the sort. Attempts to gain any sort of political power faced potentially being put down with lethal force. And the poor (and middle classes) now have a much greater chance of improving their lot than in many past societies where your lot was determined by your family.
This isn't to say the wealthy do not benefit from modern society, but to say, relative to many alternatives, one could argue that the living standard of the poor is much more increased than the wealthy. In a land of "free" education, (somewhat) free healthcare, minimum wages, worker protection laws, social safety nets, etc, etc etc are today's Western poor not much better off than the poor of the past and in many other modern societies? Compared to the rich, who are still free to enjoy lavish lifestyles, but if anything, seem to have less political clout and power over others than they used to?
Note-I am not arguing against progressive taxation here, rather saying that I find claims that the rich benefit more than the poor in modern society to be questionable.