First, in regards to the Bush Tax cuts. Saying it plumted in the 00's is kind of a dishonest statement since yes, it did take a nose dive...it also took a solid climb...followed by another dive. To blame those dives, and those raises, on the tax cuts alone (or even PRIMARILY) we'd need to assume that somehow, magically, mostly on its own, the tax cuts both significantly reduced, then raised, then reduced revenues. Or, we could suggest something occured around 2001 and 08'ish, the points where drops happened. Now, I may be crazy, but I remember two significant issues that occured had an effect on the economy. On the flip side, I don't remember any significant changes to the Bush Tax Cuts happening in '03, when the revenue began to tick up again, or '08 when it started going down again. So its it possible that rather than the Bush Tax cuts being the primary cause that it was rather exterior factors?
You're using percent of GDP. This has a few issues with regards to your logic that is implying that lower taxes are bad because it brings in less revenue. One such issue is that you're making a pure speculative assumptions that the significant negative trend of GDP growth that had been occuring for the 2 years prior to Reagan taking office wouldn't have continued. Indeed, aside from the spike in 81 (The year the tax cuts were passed), it seemed like the trend was a significant downward growth of GDP. When your GDP is lower, the ability to bring in a higher per centage of that GDP tends to be higher but that doesn't necessarily mean you're bringing in the the most revenue possible.
What's interesting, if you view the Percentage Change of GDP, as the GDP begins an uptick in 1974 you see a downtrend in Percentage of GDP in your graph. As it falls in 78 through 80, the percentage of GDP actually rises in your graph. With the higher tax rates it seems the less money that the governent took in as a percentage of said GDP.
Ultimately, looking at the rate of growth, looking at the actual GDP, looking at the total monetary values we bring in, and also looking at the relatively static state of between 15-20% of GPD, I'm unsure really that tax rates significantly in either directly provide the primary driving force that determines revenue. Outside world events affecting the economy, other government laws and regulations, and the general economic environment of the time (Such as the housing and internet boom) all I think contribute as much if not more than that. Looking back throughout your graph and the graphs on GDP and GDP growth, there's plenty examples where despite high tax rates we still saw decrease in revenue as a percent of GDP and also examples, such as part of the 80's and mid 00's where the numbers did rise year to year. I think you're exceedingly incorrect in jumping to an assumption that the tax rates in these instances were the primary driving factor.