[Joeri]

The people that I know that are self-employed and earning high incomes generally are incorporated and have an accountant to set up tax avoidance strategies to have a lower effective tax rate. Effective tax rates seem to follow a gauss curve, low at the bottom, low at the top, highest for the middle earners.

[distances]

That'll vary by country and won't be efficient everywhere in Europe. Certainly in Germany freelancers pay the same taxes as regular employees, and setting up a company means more taxes, not less.