According to the chart you posted, counting, individual taxes fell from around 14% of GDP in 1969 to 6% in 2010, a cut of nearly 50%.
Just the bottom blue part, purple is insurance (payroll) tax (which is not voluntary like your 401k, it's must pay). Red is corporate tax. Read the fine prints on the right side. Individual tax is always near 8% (to federal government). The one got cut is corporate tax. These taxes are collected separately. Like you may still need to pay the insurance tax, and in some states pay the state/local income tax.
That's hard to understand. Would you care to rephrase that?
Imagine that every person in the country earns a certain amount of money by either salary or profit from capitals (company profit, selling house, rent out rooms, etc). And assuming people all earn the same amount. Let's see if in 1960 your earning was $4000/year, then you had to paid the individual income tax of 10% for the federal government, minus some tax returns, equal to an effective tax rate 7% collected by the government. By this, each individual had to pay $4000*7% = $280. And if there were 100 million workers in US (1960), the overall production value (roughly = GDP) was $4,000*100 million = 400 billion. Thus the federal government got 7% of the 400 billion = 28 billion in income tax.
Then in 2000. If the whole GDP was 10 trillion, and the government colloected total 700 billion income tax from individual. Also there were estimate 200 million workers in the US. Hence we also got the 700/10,000 = 7% effective tax rate. Since the average earning for a worker was ($10 trillion / 200 million people) = $50,000 per year, and the real effective tax rate was still 7%. Hence each one needed to give the government $50,000*7% = $3,500 on average. (regardless what his/her income basket was). I reverse this calculate in here, for the purpose to tell that its just an over all average, and it can be calculated either way. So whether in 1960 or 2000, the worker should all feel the same effective tax rate in life, despite the huge difference in actual earnings in different time.
However people have different earnings with each other in real life too, hence different groups of income buckets have different tax rate, but on average it is 7%. Nonetheless, the composition of rich and poor are also different and changing over time, so the actually feeling although theoretically the same, people may still feel differently accordingly. The closer to current time, the richer gets richer, and most of the income tax is paid by the top 20%-income-bucket group. In effect that general population as working class would pay less and less in proportion to the rich people. I believe this is the reason why most people felt the tax is being cut for many years. (The portion got cut in middle class, was made up by the tax raised to upper class)
A large part of the growing government revenue now comes from insurance tax department, along with state/local tax. Since they're easier to raise and increase the over all revenue without touching the sensitive individual income tax. As long as people think they are paying less tax directly, people are happy. But in reality the government just take money from else where. (either in different income group, or with different reasons). The government can cut your income tax, but raise the corporate tax, hence the corporation has to sell it's products more expensive. In the end, the customers still paid the "indirect tax" through corporate tax. And the statistic about "actual tax" pressure to a working class person shows, he/she needs to paid directly or indirectly combined up to 30% tax rate from his/her income these days.