Per Koenrad Elst, referring to the original work of Talageri -
“In the Rg-Veda, the terms ‘Dasa’ and ‘Dasyu’, which are also known in ethnic meanings in Iranian languages, refer without any doubt to Iranians, i.e. fellow Indo-Europeans, whiter than or at least as white as the Vedic people. Not to Mundas or Dravidians. The Rg-Vedic Battle of the Ten Kings and Varshagira Battle (the first on the Ravi banks in West Panjab, the second beyond the Bolan Pass ..., after the westward expansion rendered possible by Vedic King Sudas's victory in the first battle), were very definitely between Iranians and Vedic Indo-Aryans. The second of these battles is also alluded to in the younger Avesta, where the same battle leaders are mentioned: Rjashva/Arjasp and Somaka/Humayaka on the Indian side, Vishtaspa/Ishtashva on the Iranian side. RV 1:122:13 mentions Ishtâshva, the Sanskrit form of Iranian "Vishtâspa", well-known as Zarathustra's royal patron: "What can Ishtâshva, Ishtarashmi or any other princes do against those who enjoy the protection (of Mitra and Varuna)?" Thus the interpretation of Sayana and SK Hodiwala, as reported by Shrikant Talageri, The Rigveda, a Historical Analysis, p.215-221, and also followed, at least in the names given, by HH Wilson and KF Geldner in their RV translations. It is a rare treat in studies of ancient literature when a single event is reported in two independent sources, which moreover represent the two opposing parties in the event."
Also, an excerpt from the previously cited link -
'In the present book (The Rigveda and the Avesta, the Final Evidence, Aditya Prakashan, Delhi), Talageri strengthens his thesis with a lot of new evidence, and refines it considerably. The master key for discerning historical expansions and migrations is the internal chronology of the Rg-Veda. Basing himself on two centuries of Western scholarship, from 19th-century German Veda scholar Oldenburg to present-day AIT champion Prof. Michael Witzel, Talageri compares the contents of the oldest layer, largely coinciding with books 6, 3 and 7; of the middle layer, books 2 and 4; and the youngest layer, comprising books 1, 5, 8, 9 and 10. Covering every verse and every instance of every category considered, and comparing the three periods, he finds a shifting focus in the names of animals, plants, rivers, landscape features, technology, ancestors, ethnic groups, and in personal name types and verse forms.
The result is of such clarity and consistency that most scholars who have been working in this field will feel envy and embarrassment at never having noticed the contours of the scenario before. It is this: the old layer was indubitably composed in the Yamuna/Sarawati region, which was to remain the centre of gravity of Vedic culture; the middle layer’s horizon expands westwards as far as the Indus; while the youngest parts are also familiar with Afghanistan. This is exactly the opposite of what the AIT predicts. In an invasionist scenario, the oldest layer would obviously be based in Afghanistan and be as yet unfamiliar with India’s interior, which would then only be settled in the younger period.
Another spectacular finding is that the early Avesta, involving Zarathustra, coincides in time with the youngest period of the Rigveda. The material and religious culture, along with the vocabulary and the name-types, allow us to link a number of datable extra-Indian connections to the youngest layer of the Rigveda. The remnants of Indo-Aryan vocabulary in the West-Asian Kassite (17th BC) and Mitanni (15th BC) culture, bequeathed by Indo-Aryan-speaking emigrant groups of at least several generations earlier, belong to the youngest period. This implies that the Rigveda must have been completed by ca. 2000 BC. "