With all due respect, Dragunov SVD 59 has maximum range at 800-1000 meters. It also fires 7.62mm and accuracy is not so popular for this rifle. In contrast, M107 or AS50 fire 12.7mm and are quite accurate. And their range is humongous 1800 meter and above. There must be a reason why they claim most of the long distance killing records.
And why can't the service keep 2 varieties of advanced sniper rifles? Is it better to let an Indian soldier die from a Pakistani Barrett M107 rather than him killing the other person? Last year, Pakistani Army was trying hard to get Desert Tech's sniper rifle so Indian complacency is hard to explain.
I am not too sure where you obtained the idea that Draganov is not so accurate and the others are accurate.
Dragonuv SVD
Weight: 9.48 lb (with scope and unloaded magazine)
10.3 lb (SVDS)
9.7 lb (SVU)
11.1 lb (SWD-M)
Cartridge: 7.62x54mmR
Effective Range: 900 yards
Feed System: 10 rd detachable box magazine
M107 .50 Caliber Long Range Sniper Rifle (LRSR)
Maximum Range 7,450 yd (6,812 m)
Maximum Effective Range 2,000 yd (1,829 m)
.50 Browning Machine Gun (12.7 x 99 mm)
Magazine Capacity 10 rounds.
The preferred load is 8 to 9 rounds.
Weight Magazine 10 rounds: 4.12 lb (1.87 kg)
8 rounds: 3.62 lb (1.64 kg)
AS50
Effective firing range 1,800 m
27 lb (12.2 kg) (no scope/sight, empty mag)
Cartridge .50 BMG
What is the weight of the M107?
A sniper operates in two man team (one is the sniper and the other with a standard rifle)
https://archive.org/details/milmanual-us-army-special-operations-sniper-training-and-employment
Check this out
Ten Best Sniper Rifles
There are many issues beyond the mere technical aspects.
To fight a war, one has to minimise the 'tail' i.e. the logistics burden. Thus, the concept of have same calibre for all direct firing weapons and weapons that are same and based on the 'add on' - 'knock off' concept, but then that is not always feasible.
Therefore, the Draganov was accepted since all weapons were in the 7.62 calibre.
.50 cal is basically ideal for an Anti Material Weapon. However, it is heavy and the ammunition is heavier and rounds carried are less. Not that a sniper is to engage in any long prolonged tactical exchange. Yet, having a lighter weapon is a boon for stealth and movement which is paramount for a sniper.
NSG choice of longer range sniper weapon is understandable since they have to operate from a distance as they will be operating in urban areas with obstacles in finding a closer optimum firing space with a clear field of view.