In fact one of the neatest pieces of real-world group polarization research examines the US legal system.
The neatest answer to these grievances would be for Spain formally to embrace federalism, with a federal senate and clear rules about who collects which taxes.
Obviously, use judgement rather than hard-and-fast rules for what looks neatest, but value clarity in appearance.
At present is the domestic scale is biggest, one of specialty technical team neatest administrative offices.