To be able to perform like that seems to me like it would take a lot of practice. The fact that they did that in Lebanon around the time of wars in the area is incredible and shows true black metal spirit. It's too bad they cannot accept that their work was evil.
I also like the two war metal bands you posted. They seem Muslim rather than Hindu, but it's hard for me to know. West Bengal is predominantly Hindu rather than Muslim.
It was a serious commitment to be a functional black metal band in Lebanon at the time they were active, no doubt. Public displays of irreligion/blasphemy come with harsh blowback in that part of the world. Add in the looming threat of war as you mentioned and it really adds a legitimacy to their music that most bands could never fathom. In a way it sort of hearkens back to what was going on in the favelas of Brazil and Columbian slums in the 80's.
The novelty alone was enough to generate a ton of hype for Damaar;
Triumph Through Spears Of Sacrilege was probably the most hyped demo since Teitanblood's
Genocide Chants To Apolokian Dawn. But it was more than that because they were clearly serious about their craft. Spirit indeed!
Most of the Kolkata bands [Brahmastrika, Necrodeity, Naramedha, Aparthiva Raktadhara, Kapala, etc.] seem to be dealing primarily in some form of Tantra or Hindu esotericism. Could be come crossover with Islamic themes as well, I'm not well versed enough to say either way.