It has been told and repeated tens of times around here:
.50 rifles are quite fine by themselves. The only problem is their abundance and abundance of .50 ammunition. I'm pretty sure every major platoon in any faction has already hoarded enough rifles and rounds to equip the whole group of BG snipers and keep them firing for a week to go.
The other thing is that not everyone is willing to do this, even given the opportunity. I know folks that find it boring and too much "old fonline"-like.
What I think is that even availability can be left as it is now, it's just a nice reason for others to invent something new against mass-DSR blobs. It may not be as easy as it sounds but it yields much more fun.
P.S. The only other thing which can be considered "abnormal" about .50 guns is their AP cost compared to SG sniper rifles. You can have 1 shot per AP pool with aimed DSR or AS50 shot, the same goes for DKS, M1C and MSG (to some extent), which are baseline SG long-range weapons of choice. With AS50, leather jacket/FLA and BRoF+fast shot you can have 2 unaimed shots per AP pool, which is also very painful as it's 2 knockdowns in a row anyway.
So heavy sniper rifles have nearly the same RoF as light ones do, yielding them considerably higher DPS of aimed shots and enormously higher DPS of unaimed shots. It'd be nice if the difference in RoF between these two groups of weapon was a little bigger, considering the range advantage and killer perks on BG rifles.