It's probably generally a bad idea to start a company in a country you intend to leave permanently. What's the point of having a company in Germany if you're not in Germany yourself?

Most companies in Germany are probably started by people who intend to stay, or are subsidiaries of international conglomerates, or have not gained enough in value to cause a significant tax burden, so the edge cases affected by the exit tax are unlikely to move the needle on business-friendliness indices like this one. (Especially in comparison to other countries with similar laws.)