The sheer size of the economy is probably not that important.
What is important is the work ethic, biz traditions, stable financial institutions.
India is lacking all those.
The really bright Indian kids from the low castes have zero chance to make it good.
Instead - they go to UK or US.
The maharajas are loaded & fat & somewhat foolish. But they control the country.
On top of that: Both India & China are going to experience the extreme social unrest for generations to come. Both of these countries are practicing selective abortions (mostly girls). As a result, the ratio of boys to girls will be around 70/30 in India and 60/40 in China.
Good luck there with your investments.
Iraq anybody?