This is great in theory, but not practice and not practiced anywhere. You could site some EU countries with a very homogeneous population and a GDP < half of the states, but it's not convincing.
I don't think we currently have the most efficient tax vs productivity situation now, but I don't agree with equality being the goal.
Obviously no argument can convince a party which say literally that proofs will be rejected, even those which might be provided on some concrete example. All the more when this party doesn’t align with the underlying praised values anyway.