I complitely agree.
But why "we" talk about "sanskritisation" phenomena if a goddess and her devotional cult are dominated by tribal elements? I would like to describe this goddesses as "tribalised", maybe because they represent a manipulation of the "mainstream" Hindu Devi, to whom are overimposed tribal elements.
If the sanskritisation (or brahmanisation) process can be described as a vertical axis where are different degrees of sanskritisation; maybe we could describe this axis with two poles: one "sanskritisation", the other "tribalisation"... obviously the dialectic between cultures bring to hybrid phenomenon, but in my opinion the Hindu-Assamese culture is widely dominated by tribal traditions, and this probably depend by ancient politic needs.
Best,
Paolo
P.S.: Maybe someone has a pdf copy of Kunal Chakrabarti "Religious Processes: The Puranas and the Making of a Regional Tradition" (2001).