Ive heard tax evasion rates were much higher historically, and that though tax rates were considersbly higher and taxes more complicated, many people simply did not pay. The simplification of taxes and reduction may have resulted in a larger amount of collected taxes.

Do you suspect if taxes were set to 99% that people would honestly pay them? To me it seems like a solution to two equations intersecting. Find the number that maximizes willing participation (a decreasing function of rates) and maximizes tax revenue (an increasing function of rates).