Another way of looking at things is in this decade we may well end up inducting only 1 Akula class SSN from Russia if at all .
In the meanwhile , all the 6 Scorpenes will be due for MLU with India make AIP from next year onwards. That means each submarine will be out of action for a good 3-4 years.
By the middle to end of the next decade all the HDW & Kilo class submarines will be retired. As it is their performance now is sub optimal give their age . By the next decade they'd barely move outside the harbour. Their replacements be it the additional 3 Scorpenes or thru the Project 75 I have yet to see the contracts being signed.
Further we'd see 2 SSNs vide Project 77 & possibly 1-2 S-5 class late next decade. So it's a mixed bag.