The linguistic complexity amongst the various states in India is very unique and hence simplistic notions of language dominance do not apply to India as a whole but varies from state to state.
Your statement that Sanskrit did not originate in the Indian Subcontinent is controversial and is not settled. But regardless, there were groups who had Sanskrit as their lingua-franca and who specialized in orally transmitting and then writing down their own (and borrowed from other cultures) philosophies and worldviews. The other linguistic groups in India did not do it to the same degree and hence you have the current situation where it appears that all knowledge only came through Sanskrit one-way. This is the fallacy that i am pointing out. Note that this is quite apart from what the content of the Sanskrit texts themselves may/may not convey; that is a different matter and has to be looked at through a different lens.