I haven't even explained to you that the genetic proof uncovered at Rakhigiri actually indicates that the people of the IVC were actually around 90% IRANIAN.
Moreover, the word "Hindu" (and its derivatives) - though Sanskrit in origin, which in itself is a non-subcontinental language belonging to the indo-European family - come from an initial PERSIAN description of people living around the Indus.
" The actual term 'hindu' first occurs, states Gavin Flood, as "a
Persiangeographical term for the people who lived beyond the river Indus (Sanskrit:
Sindhu)",
[53] more specifically in the 6th-century BCE inscription of
Darius I.
[73] The
Punjab region, called
Sapta Sindhu in the Vedas, is called
Hapta Hindu in
Zend Avesta. The 6th-century BCE inscription of Darius I mentions the province of
Hi[n]dush, referring to northwestern India.
[73][74][75] The people of India were referred to as
Hinduvān (Hindus) and
hindavī was used as the adjective for Indian in the 8th century text
Chachnama.
[75] The term 'Hindu' in these ancient records is an ethno-geographical term and did not refer to a religion.
[53][76]"
You are saying that because Vedic mutated Hinduism is somewhat similar to the original meat-eating, body burying, caste shunning animists of the IVC, that they are all of one creed and are native gangetic in origin. Do you know the origins of the modern interpretations of Christmas and Easter in Christianity? They are aberrations of European pagan beliefs, designed to permit easier transition for European pagans when the Romans imposed Christendom upon them. The concept of a holy trinity is a mechanism to permit pagan polytheism to persist in what was originally a monotheistic faith when it first emerged in Palestine (again, this "soft" polytheism persisted to enable Greeks and Romans to transition to Christianity easily).
By your reckoning, modern Christianity should be regarded as a native European pagan religion simply because it contains echoes of these pagan beliefs. This is a nonsensical interpretation of course. Christianity is Christianity, originally from the middle east, though in Europe, some pagan remnants persist as a syncretic solution.
Likewise, the Aryan peoples who migrated into the subcontinent altered the IVC's canonical beliefs so much that they were regarded as rivals or mleccha, and VEDIC Hinduism is unrecognisable from its IVC origins.
The IVC peoples ate meat (including beef), buried their dead and had no concept of caste.
Hinduism is many many things. It was born to an Iranian people in coterminous Pakistani lands. It was modified by steppe land Asiatic nomads once those Iranians declined. The things that you will struggle to declare irrefutably are that Hinduism (certainly the Vedic strand, but possibly even all Hinduism) is "native to the subcontinent" or anything to do with the gangetic plains or anything to do with the secular republic of India.