Whenever I enable aiming deadzone, the first person aiming becomes unbearable(Aim down sights). It doesn't have full movement like it does when deadzone isn't enabled. It's hard to describe, but arma2 defiantly doesn't have this issue. I always play with deadzone on, and in arma2 the aiming isn't effected by it. It isn't limited and slowed down like it is in arma3, with it enabled.
Some people may consider this minor, I even marked it as such. But to me it is a major issue, as I prefer to play with aiming deadzone enabled. And currently I'm just not able to, without severely handicapping myself.