Well, my 2 cents on this whole discussion.
1. It is idiotic to talk of India and Pakistan as 2 nations, if we talk of time before 14 August 1947 A.D. (Christian Calendar).
2. So, I will be writing in general reference to time period before 14 Aug 1947 A.D. (CC), so, I'll be writing only India and it will mean the land south to Himalayas and Hindukush, east of land where the tribe of Parsa, another tribe of Arayan people now known as Indo-Iranians, live.
3. Now, as per my understanding, we the people of India, are anciently not very keen in preserving heritage that is physical in nature with man made effort. It happened if nature wished such. Man made physical preservence of heritage came to us in 3 phases. a) In Puranic period, which is way later than the Vedic, Aranyak, Brahman (group of books, not class of people) and Upnishadic period; preservence started being done to only those physical structures which has any kind of religious meaning associated to it. b) In Islamic and Mughal period, if it was related to religion, elite or regal. c) In European colonial period (Dutch, Portuguese, French and British), it actually came to us, as westerners had developed it earlier and they not only passed it to us but also, they were the ones who started excavating and researching and discovering our long forgotten heritage for themselves and also for us.
4. Sanskrit, until Panini ( or rather couple of people before Panini whose work have been referred by him) was just a dialect and not language. But still writing was not there. So, if you refer to Aṣṭādhyāyī, you will find that it is authored with view of memorizing than being read from written text. Writing came much much later. Earliest Sanskrit matter evidence is from Kharoshthi artifacts from Gandhara and Brahmi texts on pillar edicts from Ashokan period. Even then, Vedas learning was in control of elite priest class who forbade writing it so, earliest vedic text is in Devnagri, which developed from Brahmi many hundred of years later and in between there were numerous scripts.
5. Text artifacts found in habitations near Indus are still a mystery and any speculation regarding them is just supporting some ulterior motives by some selfish or egoistic people. On them, let us wait for the truth to come out from the efforts of researchers.
6. So, in light of whatever current knowledge is available to us, it is bullshit in concluding: i) quantification of antiquity of Aryan habitation in India or Indian civilization in general based on western way of physical evidence, though, researches point towards immigration of Aryans from grasslands north to Caucasus mountains. ii) quantification of antiquity of Sanskrit again in western way of physical evidence. Though, if we go through Vedas (as I have heard from learned ones), they talk of time when man didn't know how to make fire, but they used to gather and preserve naturally occurring fire and this thing was so much necessity for the community that a separate group of people were deputed for this task and were called "Agnihotris". This made fire so precious that throughout Vedas, it is considered purest of pure and "Hotra" (linkage between Gods and Humans and also being God itself).
7. If a land is so rich in natural resources, any one who knew of it and wanting of better life would try to come to it. So, if Arayans have come, so would Shakas (Indo-Scythian), Huns or many such would come. And when some new people come and demand portion of resources, struggles or wars bound to happen. Some time home team wins and sometimes visitors win. And before European colonizers, whenever visitors won, they became part of home team. A special case of this are Islamists (Arabs, Turks, Mongols etc.), because when they won, they too became part of home team but instead of getting amalgamated fully like others, they not didn't let go their foreign origin religion but also converted thousands to their religion in any way possible.