The Hindus knew the Christian God but got Demonically led astray.

The problem is that there were many random religions there. The Ganesha Pagans worshipped the elephant God regardless. It was the Vishnu worshippers that pushed the Vedas. Shiva worshippers only took on Vedas later. As for Brahma, in a way Buddhism is linked to Brahma indirectly. Brahama Kumaris are a sort of cultish sect where they have/had the equivalent of a Pope but their take is the gods of Hinduism are largely make believe and Shiva is the most important while they prefer to skip through to Brahman itself. They think Shiva is a renwer nit destroyer.

Hindus reject them as a valid sect. Think of how JW or LDS are vs Christians that is akin to Brahmakumaris vs Hindus.

Eventually when Portuguese and Dutch showed up and tried but overall failed to rule India, they began to push Christianity more, it already was known of in the very North of India from long ago and likely influenced how Sikhism formed, as did Islam.

Hinduism stems from a nickname Persians gave the indians; Indus. Everything Indian was dubbed Indo-X or Indu. so Hinduism became how the Dutch and later Brits dubbed all the collective religions of India. They then noticed there was a trinity in it and that they could unify India under it but the Dutch had already noticed it and got the ball rolling. I am not clear what the Portuguese did. Portuguese focused more on Cath stuff and it is why South India has Catholicism a lot stronger than the rest of India because Portuguese aimed South and also at Sri Lanka which they named Ceylon first. This is also why South Indian Jindus who focus far more on Shiva, do not care as much about Vedas. They began to welcome in Christianity and Islam and prioritised peace over conflict much faster than the rest of India. They basically valued racial/ethnic-physical unity over religious unity (this was typical of South Asians and they were rigged lower on the Caste system and needed to unite as a people ignoring religion to climb up the ladder, it is also why they are not nearly as much into Bollywood or creative ventures, they learned to be disciplined doctors, engineers etc as it became either that or being a road sweeper, or something else and a life of severe poverty).

The reality is by far disproportionately the Vishnu worshippers and their Vedas are what actually formed modern Hindu theology. This is why only 44% of Hindus are vegetarian as not all shared that ideology and Shiva worshippers who see destruction as beautiful least of all cared to be vegetarians. The Brahma Kumari movement is also primarily among Saivist (shiva worshipper) heavy areas as a coubter-take on Shiva. They see Shiva not as a destroyer but a renewer and father.