Major points I could gather from the rebuttal:
- The recorded language was not "Sanskrit". There are a few Sanskrit-sounding words and a some names of seemingly Vedic-deities mentioned (along with several other non-Vedic deities).
- Some scholars even contest whether PIE was an actual language and is not just an artificial construct.
All in all, it seems to me that the writer's claim that
> Amazingly, Rigvedic Sanskrit was first recorded in inscriptions found not on the plains of India but in in what is now northern Syria.
is quite a bit far fetched. I tried locating a paper referring to the Mitanni treaties (http://sci-hub.io/10.2307/595878), but it doesn't include the text of the treaty itself (which anyway I wouldn't have been able to understand, seeing as it is not even Sanskrit). At any rate, what the HindutvavAdis seek to resurrect is mostly classical Sanskrit, which most definitely is Indian, just as English itself is, well, English, any external influences and contributions notwithstanding.
I also find these kinds of strained attacks on Hindutva extremely disingenuous and ultimately counterproductive. You want the other party to listen to you, not to shut down and shout their positions even louder, marking you as an enemy. We could begin by acknowledging some of the valid points they raise.
I for one think that there is some truth to the allegation that we (Indians) are not aware of our own intellectual traditions. I myself hadn't heard of the likes of Nagarjuna, Dharmakirti, Prabhakara, Bhartrhari, and Abhinavagupta until very recently, and I understand their theories still less.