If you have any primary sources I'd be interested,
Primary sources are contained in our Buranjis, centuries old chronicles of the Ahom Kingdom.
The Mishmi tribe of Arunachal derive their lineage to the legendary king Bhisma and through him, his daughter Rukmini and Lord Krishna. Bhismaknagar finds mention in Kalika Puran, the inscriptions found at
Tamresari temple and Bhismaknagar fort was written in Sanskrit, Assamese and Bengali script.
Malini Than temple complex in Arunachal, where the presiding Goddess is Parvati dates back to the 13th century, also houses many other deities like Indra, Surya, Ganesh, Radha/Krishna built under the patronage of then kings from Assam and Arunachal.
Parashuram Kunda on the banks of river Lohit is a place of annual pilgrimage for us in the NE, i have visited the place countless times.
Akashiganga in Arunachal is one of the 51 sacred Shakti Peeths in Hindu religion, Google it if you dont know the meaning.
There is then the historical Shiv Linga in Lower Subansiri, the Brick Fort or Itanagar(capital of Arunachal) and Bhalukpong which bears testimony of Indian cultural presence in Arunachal Pradesh.
Show us one bit of Han Chinese influence or any bits of history regarding Chinese military expedition to Arunachal, if you claim it to be China's part. Their culture is NE Indian, people speak our language with no similarity to Tibetan or Chinese, yet you make these absurd claims.
Lastly ,Donyi Polo, their ancestral religion in Arunachal can be considered a fork of Hinduism. Hope this suffices. Anyone with half a brain can make informed decisions based on these.