I don’t think the top marginal tax rate affects entrepreneurship. The highest ordered bit is cultural—Americans are entrepreneurial by nature and will start companies regardless. No one checks the tax rate first. And most operators start with little money, not $10m of income.
If marginal tax rate goes up 1%, sure, but if it went up 20 or 30%? It would seriously deter entrepreneurship. America is a big economy - it's a great market, but much in the way that some people move to Austin to reduce their tax those entrepreneurs might go elsewhere.