Culture and ancestry is always connected to the land (and DNA) and not the religion.
Just because Hinduism could not get out of the subcontinent (due to its obviously weak and unimpressive belief system) does not mean that that people of this land , who converted to other religions can not claim the heritage of the land.
This is just like saying that your atheist child doesn’t inherit your land.
Nations evolve and so does belief systems .. ancient Egyptians were not Muslims , but today they are… ancient Romans were not Christians but today they are!
Indus Valley civilization is the heritage of the people who live around the river Indus, which still flows with all its glory, in Pakistan . Most of those people are Muslims today, many are from other religions.
Shit faced Ganges dwellers have no claim on it whatsoever, just because their religion is old.
Fun fact: there are only two people in the world, who connect land to the religion.
Israelis and Hindus.