Yes. You are right. It will at least give a country like India some time to think rather than just barging in. Even then if Sri Lanka could place the S 300 system in a strategic location it will give some headache to IAF just to neutralize them.
It is better if we could get the HQ-9
Yup.
It will give some head ache ..Then there is no need for a war with Sri Lanka .
Pakistan also has Long range SAM .That is why we developed ALCM like Brahmos .