Upvote:13
The problem is not so much what they let you buy, but rather what they let you bring into the country without paying taxes. Whether you did pay taxes or not in the origin country is not relevant, the only thing that matters to them is if you paid taxes in India.
The limit of alcohol you can bring into India without paying taxes on arrival is 2 litres. As you are exceeding this allowance, you will have to pay taxes (very very expensive taxes, over 150%) for everything over those 2 litres, whether you bought it abroad and paid taxes, bought it duty free abroad, or bought it duty free in India.