There's another thing to consider here.
Does the Indian govt consider war immiment. If so then buying Aegis system would indeed be a better course of action.
If not however, it would be foolishness of the highest degree. Buying of the Aegis system with the associated missiles would mean that work on the indigenous system would be abandoned as a Technology Demonstrator or some of its lessons taken in. But for the most part, the investment put in, would be wasted.
Buying of US equipment would make India dependent on the US for this kind of system in the future as well. Everything would have to be paid for, with Indian money being used for further research in the US, putting money in the US economy as opposed to Indian economy. The further upgrades brought about by research would again have to be bought by India. It thus becomes a cycle.