A corvette is essentially a combatant.
An OPV is primarily a patrol ship.
So one is designed to fight, the other to show the flag and be ready for minor skirmishes.
Consequentially an OPV should be structurally weaker than a corvette.
But since Hisar Class ships were built with the notion of FBNW and their sea holding prowess are the same as Ada Class, they are structurally solid. Their hull construction are the same as Ada Class. But because of the FBNW design feature their internal compartmentalisation are open to conversions and addition of more weapons etc.
So the Hisar class are actually corvettes in an OPV guise. In a way they are wolves in sheep’s clothing. They are built in a more economical way to fill up the numbers missing in certain naval duties within our navy. This way we save our combatants for the more serious missions.
It is a good idea to have 4 more I-Class ships to bring the tally to 12. But the Ada Class and upgraded Hisar Class ships will be more suitable in the Sea of islands. So for the future, gradually converting Hisar Class ships in to heavily weaponised versions is more feasible.
If we are going to have a carrier and another LPD, it is better to invest in another 4 x TF2000 destroyers in the long run. (Even though they are atrociously expensive ships, if we are going to find the funds to pay for the carrier, we should prepare to spend more for a further 4 destroyers.)