There is none. Despite the less stable environment if you are Talent by far the best place to be is the US. If you are an ambitious entrepreneur by far the best place to be is the US.
You have to consider it a sample and while not fully representative, you can come to some conclusions. There are some 9 million US citizens living outside the US.
Further, you can look at past migration patterns due to political changes. Like when the Taliban took over Afghanistan, the people with the means and the smarts leave first, then the rich — unless they have a path to power in the new regime. Eventually you are left with a poor country.
The expat facebook groups have exploded if you’re looking for 'evidence'.