I have been following Indian strategic doctrine for quite sometime and more and more I analyze it more it looks haphazard and broken to me.
Think it in this manner.
1. India has not yet demonstrated MIRV and certainly not operationalized it. My question will be who are you trying to deter using such a weapon with range of 3500 to 5000 KM but no MIRV?
2. If you are targeting Pakistan, even Klub-S missile is enough, Onik P-800 is surely too much. They don't have effective counter against these. Your current deterrent is an overkill. A submarine targeting Pakistan only? That is ridiculous! If they are not deterred by your land based nuclear assets or mobile nuclear assets on TELs then why will they take your submarine based assets any more seriously?
3. If you are targeting China, then a MIRV takes priority over a single warhead weapon. Your single warhead is not going to cut it through Chinese ABMs.
4. You don't have a 'real' strategic bomb. Best you can field is a boosted nuke. May be this explains your choice to not field a MIRV. In that case, if your condition is dire enough, go test a real h-bomb and be ready to swallow some sanctions.