Go and play Platinum with the BW or the Valiant. You will see, you will dish out much less damage than the GI with Claymore, Destroyer with Harrier, Typhoon, Falcon or Piranha and Biotic classes. Due to this, Sniper Infiltrators are surpassed by those and we, Snipers, are really just doing reviving and capturing devices.
We can one shot "normal" creeps with a headshot, but against units like marauders and centurion, even a full clip of a Valiant, having perfect headshots, might not be enough. Even with the BW, I have some trouble to kill them.
But against Brutes, Ravagers, Atlases, even with TC, BW or Valiant take just 1-2 Bars of Shields/Health and compared to other weapons, it is just that pathetic. I mean, a UR and a N7 Weapon inferior to Rare Weapons? Demoralizes me to farm them.