So you wants to mean the Orientalist guys did it so many hardworks to help their arrogant counterparts who wished to bury every traces of Indian civilisation and made India a christian country. And dont forget the British had half the world in their control. Business interest was the prime factor and they did not need to justify anything to anyone.
Nope. They, first, needed to justify it to themselves. Which they did, very successfully. India a poor, beleagured nation was being civilised by the superior white man. However, when the initial studies of orientalists started revealing that perhaps India is not as uncivilised as they had thought. Missionary zeal motivated many to study other religions and cultures to better present their product and to condemn the native culture or religion.
As I said, the initial studies made quite a mark on many important minds of Europe about India's culture and religion. Suddenly, the whole narrative that India had to be civilsed by white man was being disregarded. So, new breed of orientalists were sent to work on India. They crafted the whole history of India to suit the imperial needs.
As they say, history is nothing more than set of events agreed upon by all(or atleast those that matter). Thats what happened.
After independence, the same distorted historical narrative was useful to stop 'hindu right' for the leftists and dynasty.
I really suggest you read the book of Ram Swarup. Then, you can make your own conclusions.