Flat tax is only ever flat when you hold down deductions. That’s way harder than it seems.

The corporate veil is extraordinarily valuable to the point where a minimum 10% tax on any money passing through options makes a lot of sense. However, the idea you can pass liability off for free is so pervasive you’d never get something like that to pass. Not because of how good or bad the idea is, but because of how effective voting blocks + donors are.