Even rudram 2 with lower range is hypersonic. In current scenario of dense AD, hypersonic speed is not an overkill.I do not mind that derived from part, it happens often & very reasonable. But I am not sure on the claim that a projectile derived from another projectile can retain all its previous flight characteristics including flight speed even though propulsion system can be similar. AKA, Pralay with main characteristic of Shaurya but without certain parts like the booster obviously suggest that it is intended for a role that does not require it to be send up so the next stage can kick in and sustain the flight. At higher altitude it(shaurya) will be of top speed at mach 7 range, this also is in no doubt. But that speed characteristic is not needed for the missions Pralay is intended for. So we cut down on booster & rocket motor propulsion a bit & give it a ballistic/quasi ballistic trajectory with good accuracy instead, since a tactical missile would be of useful that way?
Frankly, a 150-500km strike intended missile does not need that Shaurya like long distance high speed propulsion imo, way overkill for the cost of weapon system vs target profile. At 700-1900km reach of Shaurya, its perfect to do a time bound mission.