Every billionaire in function constitutes an aristocracy of one. Meanwhile, states have armed forces. A billionaire, in relying on money for power, implicitly also depends on continued access to the global financial system which gives money meaning, in order to exercise that power. States are not obligated to allow such access, and may easily prevent it in the limiting case by ensuring such trade comes with a side of explosives delivered at speed, which broadly suffices to deter desirable counterparties.
Think what anyone may of such a thing, the fact is having an army or navy or air force means you can do it. Which billionaire has one of those?