[yantrams]

Sure. I'll have to dig up the literature but I'd be happy to do so. Can you be more specific ?

If you are interested in investigating, It'd be illuminating to contrast the belief systems in Vedas and Puranas. (Rigveda and Puranas to be more specific. ) If my memory serves right, Narayana(Vishnu) was a minor diety in Rigveda whose only claim to fame was carrying Indra on his back to circumnavigate the universe 108 times. He gradually started gaining more prominence as time passed, as a benevolent and sophisticated alternative to replace the more belligerent/primitive Indra. By mid 15th century(I could be wrong), this process was complete, with Vishnu taking over Indra completely, as established in that Govardhanagiri tale where Indra was utterly humiliated by Krishna.

Coming to the claims on Buddhism, once again, examining the Rigvedic and post Rigvedic belief systems can help you hypothesize how things unravelled. (Replacement of Horse with Cow as the sacred animal, renouncement of non vegetarianism, incorporation of Tantric belief systems etc ) Destruction of Buddhist monasteries and massacring the monks is quite well documented too. Read about Pushyamitra Sunga for example.

Edit: Typos