Literally they did.
In 1944, the top rate peaked at 94 percent on taxable income over $200,000 ($2.5 million in today’s dollars3). That’s a high tax rate.
Over the next three decades, the top federal income tax rate remained high, never dipping below 70 percent.
https://bradfordtaxinstitute.com/Free_Resources/Federal-Inco...
Note the parent said "marginal" tax rate.
> During that period the government captured ~17-18% of GDP in taxes which is the post war average.
Even if the 17~18% of GDP is true (not saying it isn't, just dont have time to verify), it's very likely the highest tax bracket had way fewer people than it does today, so it would be equivalent of taxing earners of $100M/year in today's world. Weighing against GDP total negates increases in spending by the government to provide services that spur economies / provide benefits / etc. Point is - this figure is irrelevant and doesn't normalize the discussion.