What if the top .1% (however defined) of poor countries wouldn't have had the opportunity to exercise their talents at home? How many famous scientists would be subsistence farmers if the GDP of their country was lower?

I would guess that India gains by having rich Indians living abroad. They increase the wealth of their families still living in India, they sometimes move back to India or start businesses there. If they didn't have the opportunity to move abroad and get rich, India probably wouldn't be as wealthy.