History they say is not the absolute truth. The human interactions and desires are so complex so as to be easily comprehensible. Everyone tries to interpret the past in its own way. The science is now being used to reconstruct the past from the remnants of the things used by people in the past like the inscriptions on the stones, remains of the dead, pottery, tools used by the people of those times. History is also layered with seams representing the different chronologies.
I was going through the books at Books.google.com, reading the preview of some books on history by Romila Thapar. She seems to do the things very thoroughly and putting across these very legibly. Theories of invasion of North India and then whole of Gangetic plains during the course of time also lack evidence and are not fully convincing.
Another book detailing the history of Maratha people by an British author who spent considerable time in India tells us that it was easy for the Aryans to spread across the Ganges plains because of easy terrain and fertile land for agriculture and availability of water for survival. After reaching and settling up to East of India, they moved towards South India across the Vindiyas. This delay seems due to difficult terrain dividing the south and north of India.
But their entry into the Maharashtra was the last.