Another argument against what you are saying here is that when you look at the Eastern vs Western Roman empires, the Eastern Empire had more progressive tax pol

Another argument against what you are saying here is that when you look at the Eastern vs Western Roman empires, the Eastern Empire had more progressive tax policies, and was more effective at imposing and collecting taxes on the wealthy than the Western Empire was. As a result the tax base in the Western Empire was very narrow, and this contributed to its collapse (at the time the Goths overran, the Western Empire was collecting less in taxes than the Eastern Empire was spending on defence). The relationship between taxes and prosperity is a complex one, but if we go by that example, it seems that an active policy of reducing concentration of wealth is the best way to ensure common defence and joint prosperity.