There are many issues with turn speed for players and AI.
Able to turn around with any amount of gear in an instant, results in spinning around like a madman. This is the case whether standing, crouched or prone, with any weapon.
Heavy weapons have lost aiming intertia like they had in ARMA 2 (M107 notable example)
Aiming deadzone is broken (instant full speed acceleration, this is bad because aiming deadzone now can't be used for fine-tuned aiming adjustments - THIS IS A NECESSARY MECHANIC FOR AIMING DEADZONE)
I have seen AI to multiple complete 360 degree rotations
AI "locks on" to your location instantly
AI do not scan horizon, once they know where you are roughly, they lock on and start shooting
AI are able to turn around and shoot faster than a player can react