“but i think this perspective also ignores the fact that hinduism in its most ancient and pagan forms was shaped by dalit and adivasi communities and later appropriated by savarnas with rules and rituals (caste) created to their advantage”
I would be very interested in reading more about this topic, do you have any recommendations for where to start? thank you in advance
A Panoramic View of Tribal-Hindu Cultural Interface by Sandhya Jain.
The Hindus: An Alternative History by Wendy Doniger.
These are the most comprehensive books on the subject. However for a deeper understanding I think the best approach is to read the history of ancient India from a neutral perspective, read between the lines to understand the consequent processes of Aryanisation, Sanskritisation and Bramhinisation, and draw your own conclusions from that.
A History of Ancient and Early Medieval India: From the Stone Age to the 12th Century by Upinder Singh - the most detailed and the best.
India's Ancient Past by R.S. Sharma for a compact overview you don't have the time and patience for Upinder Singh.
Early indians: From Origins to AD 1300 by Romila Thapar - great for socioeconomic analysis of ancient India.
Early Indians: The Story of Our Ancestors and Where We Came From by Tony Joseph.
I also recommend reading up on the history of Tantra which is heavily influenced by adivasi practices, kept alive and still largely practiced among oppressed castes: History of the Tantric religion by N.N. Bannerjee.
These should be enough to give you a general idea about how the Aryans appropriated and eventually subsumed older religions and traditions under the broader umbrella of the vedic religion.
For more localised narratives -
The Cult of Jagannath and the Regional Tradition of Orissa by Anncharlott Eschmann, Hermann Kulke and Gaya Charan Tripathi. The writers use the example of the Jagannath cult to deliberate on the transition from tribal culture to Brahmanisation of the deities and focus on some Hindu temples which have been constructed at places where tribal deities were being worshipped since time immemorial. They also discuss deities like Charchika, Bhattarika, Pathalika, Badamba, Maninageswari and Tarini, which were originally tribal deities of Orissa that were gradually incorporated into vedic gods and goddesses.
The appropriation of Murugan into Karthik has been much better documented.
The Rise of Mahasena: The Transformation of Skanda-Karttikeya in North India from the Kusana to Gupta Empires by Richard D. Mann.
The Many Faces of Murukan: The History and Meaning of a South Indian God by Fred Clothey.
The Cult of Skanda-Kartikeya in Ancient India by A.K. Chatterjee.
The Book of Kali by Seema Mohanty.
Revisiting Kali: An Amalgam of Aboriginal Deities and a Symbol of Rebellion by Sumanta Bannerjee.
Banglar Daakat Kali: Myth o Itihash by Pinaki Biswas (this is in Bengali, I couldn't find a translation unfortunately but on the off chance that you can read Bengali I highly recommend this)
In Bengal, Kali is considered a saviour and protector of the downtrodden, and a manifestation of rage and resistance symbolised in blood. The more violent forms of Kali are the ones more similar to the tribal deities she was appropriated from are still primarily worshipped by Dalits.
Shoshan Kali (Shoshan literally translated to burning place) is a form of Kali that is primarily worshipped by the people of the Dom caste - undertakers responsible for disposing of the dead. Shoshan Kali is considered a patron of the space between the living and the dead, which is also why Bhoot Chaturdarshi, another folk festival honoring spirits and ghosts (Bengal's Halloween if you will) is celebrated the day before Kali Puja. It is also worth noting that animal sacrifice, red meat, blood and alcohol is mandatory in the worship of Shoshan Kali; which goes against vedic savarna sensibilities - which is probably why upper castes had always kept their distance from Kali until very recently in the last century.
Kosai Kali is a patron saint of the butcher castes - the Khatiks and Budhiks (who are now classified under SC). In 17th-18th century Bengal, hindus could not eat meat unless they had been offered to a god first and thus purified - which meant that meat was only consumed as prasad after pujas. The butchers initially opened to cater to muslims who could eat meat all year round but they wanted to expand their business, so they came up with a workaround. They installed an icon of Kali in the shop and performed a puja every day before opening shop thus purifying the meat they were about to sell - which meant that hindus could now consume meat all year round, thus forever changing eating habits of Bengal. Even today, butchers in North Kolkata perform a daily puja for Kosai Kali before opening shop.
The Sacred Bond: Lord Shiva and Aadivasi Folklore in Indian Mythology by Sheetal Kakar
How Tribal India Has Held Onto Shiva by Nabarun Barooah.
Something I have observed is that the further away from the vedas the practices get, the more it seems to belong to Dalit hindus. Most of the non-vedic deities from Bengal are not worshipped by Brahmins. Manasa (bengali folk goddess associated with snakes), Sitala (folk goddess believed to cure smallpox and other diseases), Oladevi (goddess of cholera), and Shashthi (folk goddess of fertility and protecter of children) and mostly worshipped by the women of the household. The mantras are all in Bengali, not Sanskrit, and the rituals can be performed by anyone, it does not require brahmins to complete the absolutions. This can partly be explained by the fact that village economy is dictated by caste and the poorer lower caste people living in mud households are way more likely to be bitten by snakes, or have their children die of smallpox or cholera; compared to upper castes who lived in better protected houses and could afford better healthcare. But also, they are most likely derived from earlier fertility and/or protective goddess from a more pagan past, which has (mostly) escaped Sanskritisation.
Dharmathakur or Dharmaraj is a folk deity from Bengal worshipped mainly by Dalits, especially the Bauris, Bagdis, Dom and Chandala castes. Dharmaraj is considered to be formless, and represented with a sacred stone daubed with sindoor. There have been attempts to link Dharmaraj with various Vedic gods like Shiva, Surya, Yama etc. and bring him under the vedic umbrella but somehow, perhaps because his worship has always remained exclusive to Dalits, he has always resisted appropriation. Over time, Dharmaraj also came to be closely associated with Sufi traditions in Bengal - as most likely Dalit hindus converted to Islam but did not entirely let go of older rituals and worship but rather fused them with each other. Which is why many of Dharmaraj's representative stones double as Pir sthans (which is Bengal's version of Dargahs). Dharmaraj's vahan (carrier) is a horse, which is why you will find clay horses daubed in sindoor in almost all Pir sthans in Bengal - even those that do not have Dharmaraj's stone. Also fun fact, Dharmatala, the central area of Kolkata is named after him.
Charak Puja or Gajan is a folk festival from rural Bengal intended to honor Dharmathakur in some places, Shiva in others. It is mostly considered a festival of lower castes as the rituals are deemed too difficult and undignified for upper castes to perform. They involve rolling in the dirt, self-flagellation and swallowing fire in a display of frenzied devotion. (Off topic trivia but it has been said that Charak Puja's rituals may have been influenced by Muharram processions. Though I personally doubt it considering Shia muslims in Bengal were always a small community who mostly lived in cities and Charak Puja is a rural festival, but it is possible).
Rankini is another non-vedic deity worshipped by many of the adivasi tribes in Jharkhand and Bengal. Her shrines are usually found deep in the forests and like Dharmaraj, she is considered formless and depicted as a stone. There have been attempts to incorporate her as a form of Durga and Kali but, perhaps because the aadivasi tribes in the east have themselves largely succeeded in resisting appropriation and assimilation by the Aryans, Rankini too has escaped Sanskritisation altogether.
Bonbibi, believed to be the guardian spirit of the Sunderbans, is worshipped by both Hindus and Muslims alike in the (dalit) fishing communities of the Sunderbans.
Offering Flowers, Feeding Skulls: Popular Goddess Worship in West Bengal by June McDaniel.
Historical Studies in the Cult of the Goddess Manasa (A Socio-Cultural Study) by Pradyot Kumar Maity
Cult of Goddess Sitala in Bengal: An enquiry into folk culture by Subrata Kumar Mukhopadhyay
The Cult of Bonbibi: A Folk Paradigm in Deltaic Sundarbans by Kakali Chakravarty
Rankini: Devi, Myth, Manabi by Kaushik Dutta. (this is in Bengali)
Rarher Sanskriti O Dharmaraj by Amalendu Mitra (also in Bengali)
If you can read Bengali please do read Banglar Loukik Debota by Gopalkrishna Basu. I can't recommend this book enough because of all the books listed this one goes into the deepest dive into how most of the Vedic gods were most likely appropriated from earlier deities that existed in the land; However, most of Bengal's folk dieties resisted appropriation and were only be included in the vedic milleu either as lesser gods like Manasa, or appropriated as the occasional form of a Vedic god, as happened with Shashthi, Sitala, Dharmaraj and Jagannath. Some, like Rankini, or the Santhal's Bonga pantheon, resisted Sanskritisation altogether.
Again, as I mentioned earlier the best approach to this is to read neutral accounts of history, read between the lines and draw your own interpretations, which is what I did. If you are specifically interested in Bengal then read Banglar Itihas: Adiparba by Niharranjan Dey first. Here is a translation by John W. Wood.
Apologies for a large part of this being specific to Bengal and for the many untranslated books. I do feel that the Dravidians have been a lot more successful in preserving their pre-vedic past, but my knowledge of it is mostly surface level so I'm not going into it.
Tagging @murukanism here in case you want to add anything or have anything to recommend, since I know this to be a topic that interests you too. :)