I love shotguns, but against more powerful enemies a sniper just simply deals more damage with minimal risk. A critical just deals so much from a decent sniper that it is hard to compare it to any of the shotguns. Snipers also tend to be less risky shooting an enemy (especially a powerful one) from afar is way safer then having to run up to their face in order to deal the maximum amount of damage. This is especially apparent when something like light switch is on, a shotgun could take on enemies one at a time easily even with light switch, but if you get say three around you, a shotgun does not fire faster then those enemies can melee you so you are screwed. You are just simply better off staying away from them and picking them off before they get near.