Uh, the poster was talking about records so I picked the (recent) record year.
Do you agree that current revenue collections aren't close to the record on a normalized basis?
True. But, you should have pointed out that 2000 has been exceeded only one time in the last 75 years - in 1945, when we still had wage and price controls, and the war ended.
Personally, I see no value in finding the ratio between federal tax revenues and GDP.
Close to one third of tax revenues come from state and local taxes. Right now, I'm staring at a total tax revenue chart, and the tax percentage of GDP in 2008 (first year of the Great Recession) is equal to the tax percentage in 2016, eight years into the recovery. How does that add to our understanding about anything?
However, I do think it is helpful to see the inflation adjusted per capita GDP compared to inflation adjusted per capita tax revenue and per capita government expenditures. I used to make my own charts for those data ratios back in the 1990s when I was day trading.
Finally, it is never obvious on these charts if Social Security and Medicare taxes are included or not. That's important, because those revenues are NOT invested. They are instantly borrowed and spent by other federal agencies.