First, what is the accuracy of their MLRS? Normal ballistic missiles with INS still have a rough accuracy of 40-80m CEP (And that means 50% probability missile will fall within the radius of 40-80 from target).
And that is the reason, artillery is always used in barrages, to increase the probability of shells/missiles landing on the correct target.
However, in the mountains, 80m offset means a huge distance and can mean more than 160 mtrs away.
Plus, mountain acts as a natural barrier, offering numerous natural bunkers/shelters in form of terrain, rocks, and crevices.
Steep valleys of Ladakh are very difficult to accurately target with artillery unless it has a top-down approach like cruise missile BrahMos.
But wait, don't just fall for the heavily exaggerated figure of range just yet!
Let's look at the claimed rocket first.
PCL 191
Notice the length of the missile ~ 6-7m.
Now look at BM-30 Smerch, Soviet MLRS
Length of the missile - 7.2m, thickness - 0.3m, range ~ 70-90km, warhead - 243kg.
Indian Prahaar missile -
Length of the missile - 7.3m, thickness - 0.42m, range ~ 150km, warhead - 200kg.
Now look at PC-191 claimed range - 350 km for a thickness of 0.35m.
Which means Prahaar has 35% more fuel space than PC-191 but has less than half the range of PC-191?
So, either PC-191 is carrying a grenade as a warhead, or this is just Chinese propaganda.