I don't like spending this much time arguing against campism but they just keep talking at me.
If a socialist/communist society were working, there wouldn't be any billionaires. In fact, if Capitalism were working, there wouldn't be billionaires. There's literally only two systems that have ever been capable of tolerating that kind of inequality. The mercantile system of feudal states, and the neo-mercantile system of Fascism. The very existence of billionaires is proof of dysfunction in every other economic paradigm.