There is no such thing as a subcontinent when the Europeans came. There was only India the land of spices that Europeans set sail for. And according to their knowledge, it's a quadrilaterally shaped country. Didn't care what all kingdoms existed in the quadrilateral.
Diversity my foot, all the countries in the world are diverse in one way or the other. You can't have a country that has no diversity. Diversity is a strength in the formation of a strong nation, India has no prospect if it were to be small nations. Our strength is our area, population, and the resources we hold.
Of the three brothers formed out of British India, who is doing fairly better? Small nations neither have the capacity or any relevant industries to be the growth engine of the region right now.
On topic, Bangladesh faired better than Pakistan despite a 25-year gap between Brit independence and liberation is because you avoided conflict with India, but if you are looking for one, it'll not be very nice for you. Modi is the PM of India, he is not the RSS chief and if you want to give in to a bunch of Islamists then good luck to you.