You do realize you went from talking about the time it takes to line up shots with a Scout Rifle, to how it's easy to deal with hordes using Firefly, a fairly rare perk. My point stands. It's more difficult to land a head shot with a Scout Rifle in most of the situations you run into during PVE than it is with an AR. As for Hand Cannons, they are a bit easier to use if you've got a good one with the right perks.