You posted a video of a completely different weapon to make your point, I posted that video to show you the actual weapon being used in a way you said should be impossible. The GM-6 is a bullpup and has a recoil absorbing barrel system, it's specifically designed to be easier to handle than that beast you posted.No, it's likely he isn't hitting much of anything, but this is definitely modelled in game. While standing, weapon sway makes even a 200m stationary man sized target difficult to hit in a timely fashion. Moving? Forget it.
If you're using this weapon to "snipe" at that range, you're completely wasting it anyway. That's not even sharpshooter territory. If you can run around and quick scope targets at 500m, 800m and 1000m I'll eat my hat.