The solution is just not that complicated:

1. For individuals, simple tax code which does not distinguish where your income came from, but does keep income brackets (not flat tax).

2. For businesses, distinguish between:

- "US-based" company which would pay 10% corporate tax. A US-based company would need to have at least 66% of employees based in the US and/or at least 50% of the products/services produced in the US.

- "international" company would pay 35% corporate tax, if they want to do business in the US.