You’re thinking about this narrowly. The broader implication is rising income inequality. It’s not sustainable. If GINI gets too high it can only end in reform, revolution, or anarchy.
The idea that billionaire returns are required for motivation is laughable. 99% of people are similarly motivated by a $10M return as a $1B return. The point is not necessarily to rid ourselves of capitalism entirely (though that’s logically the optimal outcome in the long run, since by definition capitalism’s optimization function is independent from socially or even individually desired outcomes), but rather to bring compensation disparity down to a reasonable level. I’d recommend targeting a GINI of .3 to start, if you want to put a number on things.