The US also kept much higher marginal tax rates for a few more decades after that, which helped the common people by disincentivizing the post-Reagan short-term-financial-games profit-maximization and wealth-and-income-consolidation.
Like in 1947 a factory owner's profits would show up as high income. Today they wouldn't (money is in share prices and complex financial arrangements / borrowing). The high marginal rates hit the chief engineer instead, who actually works for a living.
But it's also disingenuous to claim that none of today's approaches would show up as high income. A lot of old money would be protected still, a lot of new-money would be hit.
Isn't it telling that there was so much massive development of American industry in the post-WWII era and yet there weren't any Musks or Bezos or Gates? A country that had minted tycoons like Getty and Rockefeller and Carnegie stopped for a while. A guy like Howard Hughes was involved in several areas of development but didn't touch the guys who came before him or after him overall...
It is pretty absurd that one can borrow against a mountain of owned stocks and live of the loan without it being considered income.
The burger is taken from the poorest person that was able to buy a burger. Now you have 2 people who cannot buy a burger.
This is why you cannot tax unrealized gains. You are sacking the poorest. Is not matter of how the government gets the money. The problem is that the government spends the money.
The poorest always pay all government spending. Always.
Apparently you can buy islands, super yachts and more with unrealized gains.
You can take out a loan secured with assets as collateral, but you're buying something with that debt not unrealized gains. If your asset prices go to zero you still own the yacht because you still owe that debt.
Get sloppy and we end up with more loopholes and bullshit.
It's called "the marginal propensity to consume", which means that as a person gets richer, consumes a smaller percentage of his fortune.
This is a common trope, but it ignores that at the time the tax code had loopholes that could smuggle a freight train full of gold bars. Instead of lower marginal rates, people were taking their real estate and personal vehicles and everything else as tax deductions, and then weren't paying the high marginal rates to begin with. The lowering of marginal rates came with the closing of most of those loopholes, which is why the change had no real effect on federal receipts as a percent of GDP, which has been in the same range since the end of WWII (and was much lower before it):
https://fred.stlouisfed.org/series/FYFRGDA188S
The thing that actually changed is that markets have consolidated a lot more than they were in the mid 20th century, and we have significantly more regulatory capture where e.g. corporations lobby to make their services required by law or to impede or prohibit new entrants to the market. Then consumers/workers have to pay more for those things while receiving nothing of value in return. Corporations take more money and it comes from labor.
Increasing the tax rate doesn't fix that because you'd still have workers paying the high prices to corporations even if the government subsequently took more of the money.
What happens if you have to buy a product from a monopolist so they currently take your last $100, and then the government comes and says they have to pay 80% of it in tax? Best case the government gives the money directly to you, but then there is still a monopoly, so they just raise the price by the amount it takes to extract all of your money again. Worst case, the money doesn't go to you, it goes to some cronies who will now be using it to lobby to increase the amount you pay, and have just demonstrated that they're more politically connected than the original corporations.
To actually fix it you have to get back to competitive markets, efficiency and low barriers to entry.
I have half-jokingly wish a president would introduce a 95% tax bracket at some ridiculous number so this statistic will die.
The highest effective tax rate was in the 70's.