Think again. How do I or you know that they indeed have blankets of SAM ready? Just because they mass produce everything doesn't mean they essentially have that impossible and impenetrable layer of SAMs. Besides, 90% of their batteries are in their east coast facing Japan, Korea and Pacific side against US... similar to how our southern side is the least armed.
The main advantage of Nirbhay is that it comes very cheap compared to BrahMos. Add economies of scale to it (3,000+ easily, since we have been acquiring more than 2,000 BrahMos itself) and you have a thundercloud of cruise missiles. One thing you must remember; any weapon system in our scenario is developed not for 1 theater alone; it is for everything. Cruise missiles are the only types of missiles that can be used in a first level escalation without resulting in a nuclear fall out. So expect Nirbhays to be used en masse.
Shaurya's purpose is not the same as Nirbhay. Shaurya is a tactical ballistic missile that doubles as a quasi-cruise missile as well. It is a second strike capable missile that is not exactly meant for taking out columns of enemies or artillery or tank columns. Its objective is seek out high valued military assets and pulverize them such as advanced forward command and control centers, regional command HQ, forward communication links and even hoards of infantry enemy troops.
Around 3,000 supersonic versions as mentioned in some analysis about a year back. Hypersonic version, no updates. See the point of Nirbhays would be to be used exhaustively while BrahMos would be kept for much more critical targets. A Nirbhay as per what estimates are made is going to cost less than a fourth of a BrahMos (excluding economies of scale, which will make it even cheaper to operate and use).