We know of quite a number of large scale migrations into India, I don't know why we should doubt that the Indo-European entry into India contributed significant

We know of quite a number of large scale migrations into India, I don't know why we should doubt that the Indo-European entry into India contributed significant genetic material. I know there are some fairly recent studies on the actual genetic DNA material linking Indians with Europeans, but I'll have to dig these up (the language side is my area; not the genetic side). The place of milk in especially early north Indian culture (but continuing into today, esp. say in the Punjab) is not like ice cream parlours in China or whatever. It is quite clear that a large percentage of caloric intake would have been from milk products, and seemingly not primarily cheese, but milk/cream and butter/ghee. The prominence of milk products in India for the last few thousand years is not at all in doubt (and, again, not in the sense of eating the occasional ice cream and farting). No-one is saying that Indo-Aryan was the first language in India, so I don't know where you're bringing that in from. The Dravidian speakers emigrated into India either around the same time or before the Indo-Aryans, and the Munda speakers seem to have been there earlier than either, and it is quite clear that there was at least one other language family well established in India before the Munda speakers entered (quite possible multiple language families) as attested by the large percentage of words of completely unknown origin in languages like Hindi for agriculture/crops, as well as the languages of the Andaman islands.