I think we need to look at this as a game first, a simulation second.
Nobody said that deviation was a realistic representation of ballistics, what deviation does give you however is the ability to tailor weapons to specific roles, and to control the ways in which players fight.
One of the most shining examples of deviations glory is the current misc deviation added when jumping and going prone. That single change has damn near eradicated the dolphin diving problem in the game.
Deviation is used when players are moving to make their shots less accurate, forcing them to stop, or zoom in to lay down accurate fire. I have no personal problems with the accuracy of the shots, I like my rifle shooting where I place my sights, what I would like to see though is the subtraction times increased.
Currently players can run up at quick speeds, and quickly hit crouch to collapse the crosshair to a near pin-point shot, this means that without zooming in players can quickly and instantly engage targets with a rifle, even after having ran or sprint a long distance. I would like to see the subtraction rate on the move deviation decreased, so that when players crouch or stop, they have to, if I will go so boldly, "catch their breath" to lay down accurate fire. This would prevent people from running into open areas, knowing them can quickly crouch to engage targets, and instead would encourage them to move from cover to cover instead, knowing that as they stop, they wont be able to lay down fire immediately. In addition the lowered subtraction rate on the rifles would allow iron sights to take more precedence over unzoomed fire. Players would find that zooming in would give them a better chance of hitting their targets quickly, but for that accuracy they sacrifice their movement speed, and thus players will get behind cover and utilize their iron sights before just randomly pulling the trigger.