I suspect very few billionaires are involved with their lowest level workers pay rates. People working for minimum wage are mostly working in franchised fast food places and such. The people determining their pay rate are far from millionaires much less billionaires. Typically, they are manager/owners who may have one tier of assistant managers above the lowest paid workers. The amount they pay their lowest paid people comes right out of their bottom line and thus their income. Any of them could decide to pay their workers more, if they want less.
In a larger corporations, there are managers who have an incentive to show their labor costs as low as possible to please higher management. There is a whole game theory area about how much to pay people versus turnover costs. The CEO hardly ever gets involved, unless they want to push a particular agenda for political or PR reasons.
So I think a 72% top rate on incomes over $10 million may be something that is workable. Bring back the estate tax, too, on estates over $10 million. 72% would be fine for that too. Nobody's kids need more than $10 million to start something productive. Over that just enables stuff like Trump's daddy leaving him 100's of millions to squander on idiotic vanity projects.