Apropos of your observations, you might find the following
LINK from the WSJ of interest - in particular, Hauser's Law. In essence, despite changes in tax rates, total revenue tends to stay at about 19% of GDP.
The article suggests that revenue projections above this rate will tend to be overly optimistic, implying further increases in national debt.
The relationship is not free of controversy; a search on Hauser's Law will reveal strong supporters and opponents.