I was married into a TamBram family, and after a while you can just clock Iyers vs Iyengars (which is a hyperfine distinction if there ever was one). It’s based on names, differences in pronunciation, items of jewelry… Those are like the differences between a Londoner and somebody from Oxford.
But a Bengali or a Gujurati? They look totally different, like the difference between Connor McGregor and Al Pacino.
India is a BIG place, it has only ever been unified as an empire, never as a nation.