How would they take more from the billionaire? Means test them? What if they're asset rich, cash poor... or if they have no income?
The whole idea is unworkable. It's like it's been dreamed up by a 5 year old.
In the current system, yes. But at least we do away with one set of means testing. I would actually argue for a flat tax rate in the presence of a basic income. As for "asset rich, cash poor, no income" there are plenty of ideas out there for capital or capital gains taxes.
We have this obscure system that has been around for a few thousand years to do this. It's called "taxes".