Your hypothesis is not supported by actual evidence.
Google the richest 10 countries in the world.
They all have tax brackets.
When I worked as a high class engineer with a master’s degree in mechanical engineering, I learned very quickly, to pay little attention to theory, and pay lot more attention to actual results.
When the theory is the theory of Marx and Engels, you would be well-advised to pay attention.
A graduated income tax is essential to the imposition of Marxism/Socialism.