In 1944, the top rate peaked at 94 percent on taxable income over $200,000 ($2.5 million in today’s dollars). That’s a high tax rate.
It sounds like a high rate, but it wasn't the effective rate. The Individual Income Tax Act of 1944 PDF specified a tax of $156,820 for net income of $200,000 (78.41%) and 91% for excess over $200,000.
It also set an overall limit: "The tax imposed by this section and section 11, computed without regard to the credits provided in sections 31, 32 and 35, shall in no event exceed in the aggregate 90 per centum of the net income of the taxpayer for the taxable year."
The rate alone doesn't explain much without looking at the exemptions. For example, parents did not have to count income received as a result of their working children. Of more interest to the oligarchs, trade and business deductions, work-related travel and lodging expenses, rent and royalties deductions, depreciation and depletion, losses from sales or exchange, charitable contributions, medical expenses, capital losses all provided opportunities to reduce the amount of net income exposed to the tax rate.
Collections are also dependent on enforcement. I doubt that the tax-avoidance schemes we hear about today are much more effective than those used in the past.