The 3DR gimbal, as well most other 3-axis gimbals use the yaw axis/motor to smooth and stabilize the yaw axis. The operator does not have direct control of the gimbal yaw. It is just there to remove shakes and smooth out the copter's yaw changes. If the operators to pan the camera, the operator yaws the copter, not the camera. A 2-axis gimbal will not have that ability. So copter yaw is directly visible in the video, no matter how smooth or jerky it is.
There are some high end professional gimbals that are designed the user to control the camera yaw, use slip-rings to allow continuous motion, and the copter yaws totally separately. These are often used in dual operator professional rigs, where one guy flies the copter and the other is in 100% control of the camera in all axes. That is NOT the solo.