I'm afraid it really is a case of practice, practice and then some more practice. There is absolutely no substitute for stick time.
The reason it can not be made more 'smooth' as you say is because of the way follow mode works. (All three axis follow mode gimbals are the same).
There is what's known as the 'deadband' which is usually a range of +/- 5degrees around center point. This deadband floats around the center to absorb lateral movements of the craft. You will see this if you lift up your Inspire when it's powered up and then turn it from side to side. This movement nullifies the undesired yawing when in flight and keeps the image stable around that axis.
However, the deadband must move when the user inputs a yaw command and this is where some clever mathematics goes on to decellerate the gimbal as it approaches its limits of the deadband. If this area was made wider or the reaction slower you would lose the ability of the gimbal to counteract lateral drift movements and any yaw input would be very sloppy to respond.
It is a fine balancing act of PID values to tune a gimbal to be as steady and at the same time responsive as the X3.
Hope that (sort of) helps.
Practice and then practice those feathered yaws some more!!!!!