Given that:

• specialists agree that Avestan and Sanskrit are remarkably close in morphology and syntax, to the extent that one can often be transformed into the other by the mechanical application of sound change laws; and

• the exact place of Avestan within the Iranian tree is problematical (e.g., Avestan’s classification as East Iranian is based more on its dissimilarity to West Iranian than to any close affinity to other East Iranian languages)

the theory goes that the Avestas (and by extension, Zoroastrianism) originated among Indic speakers and then spread to Iranians, who adapted the original Sanskrit to Iranian phonology but otherwise left it unchanged. This would make Avestan an Iranized dialect of Sanskrit, rather than a true Iranian language.

This in turn would imply that:

• our reconstruction of Proto-Iranian has been distorted by the inclusion of Avestan;

• the grouping of Indic and Iranian into an Indo-Iranian sub-family is based on this faulty reconstruction;

• the similarity of deities and religious terminology is due to the adoption by Iranians of an Indic religion, rather than to a common cultural inheritance; and

• Indic and Iranian speakers may have had different migration paths from the PIE heartland.

Has this theory been addressed somewhere? I assume there’s a reason it doesn’t seem to have caught on with Indo-Iranian specialists.