> India would be more than 1000 years behind today

Behind what? And what are you basing this on, other than vibes and your biases?

> without external influence

Of course it would be externally influenced, even without being colonized. It isn't an island. It couldn't shut itself away like Japan did pre-19th century. Japan is more modern than India because it wasn't colonized. They just took ideas from abroad - industrialization, mass literacy, (some) democracy (pre-WW2) - and adopted them.

> Okay, but it's also a huge country the size of a continent

And India isn't?