It is not certain that Maga Zarasabdha was Persian Magi Zarathustra. Some scholars claim that ZaratkAru,a Naga vanshi, described in Maha Bharat, Aadi parva, chapt. 5, may be Zarathustra. But it is certain that Magh was a very powerful tribe of ancient India described in Rig Veda. The term like Maghoni/ Maghan/ Maghor/ or simply Magh appears at several places in RigVeda ( e.g. yo vanita magham RV.3.13.3). Indra is also designated as Maghvan at several places and it is wrongly interpreted as rich man, whereas internal analysis easly establishes this term as a tribe not riches.
This ancient tribe Magh migrated to far off places may be upto Egypt because in ancient Sumerian language Egypt was known as Maghan. The ancient Persian Magh/Magi/Magu is certainly Rig Vedic Magh because they also worshiped many Rig Vedic god like Mitra,Yima/yam,Airyaman/Aryaman, and remember Verethragna(Indra)etc. Persians also called their fire priest as Atharvan.(see www.iranicaonline.org).
One of the important hymn of RigVeda describes Atharvan as the messenger of people who settled in far off places and he/they used to visit them for the work of Yama -
agnirjAto atharvanA vidatvishvani kAvyA
bhuvat duto vivasvato vi vo made priyo yamasya kAmyo vivakshase
(born of Agni/fire Atharvan knows the book of world, became messenger of people settled out side and for the purpose of Yama's work move out happily.)
The movement of Atharvan to other land is also supported by Persian text. Encyclopaedia Iranica (www.iranicaonline.org/Atharvan) writes- "The oldest attestation of the word Atharvan is in the Yasna Haptanhaiti where the worshippers honor 'the return of the priests who go afar ( to those who ) seek righteousness in other land' that is, it seems to Atharvan acting as Zoroastrian missionaries." Missionaries or messenger depends on interpretation, but Atharvan were going to other land.
Historians(mostly Marxists) claim that the story of Rig Veda did not occured in India, but somewhere in Central Asia, despite the fact that Rig Vedic geography is that of India. Some of them argue, that's why the greatest god of Rig Veda Indra has no place in Hindu religious worshiping, while minor god like Vishnu have a highest place.