Becoming a billionaire is never done through your hard work.

It is only by exploiting the surplus of large amounts of workers at scale that permits being a billionaire. It is their hard work, not the billionaires.

Now, how much surplus the workers get is primarily the discussion between capitalism, socialism, and communism.

Naturally, capitalists are disinclined in giving ANY of the surplus, and keeping it all for themselves. But when every capitalist does that, thats how we end up with 7 year depression/boom cycles, when the whole economy treats workers poorly.