Why do you assume counterparties grow exponentially with wealth?
This would also only apply to that portion of the tax burden associated with enforcing contracts (a very small fraction, basically just the police and judicial system).
The police and judicial system don't exist in vacuum. And where does the power of the judicial system and police come from in modern time? From the people. And what is the cost for them to grant power to such a system? A functional society that they feel supporting.
Our tax is not just funding for the judicial system so that the rich can get their properties protected. Our tax is funding a functional society that's the basis for all these.
This would also only apply to that portion of the tax burden associated with enforcing contracts (a very small fraction, basically just the police and judicial system).