The main question in my opinion is that should one give serious consideration to the Hindutva School of Historical Thought

There are few points I would say : It is pretty clear that Koenraad Elst is one of those historians who can be clubbed in the category of Hindutva Historians. The problem in his writing as well as that of the whole Hindutva School of thought is that it is highly politicized, the intention of their writings is less for the purpose of academics and more intent in scoring political brownie points(for a certain ideology). For eg: His works on the Ayodhya Dispute

Last but not the least If you are a scholar/researcher then it is imperative that you have an opinion about historical events (like Aryan Invasion Theory: Did it happen or as a Hindutva historian would say it was the fabrication of the British )

But if you are a student of history then in my opinion you should accept the standard view that is agreed upon( in this case Aryan Invasion theory did happen).

As is the case of reliability(esp. in history) "Men believe what they want to believe"