I have performed a number of experiments using Litchi and an Air 2s trying to obtain a smooth yaw movement as the drone proceeds through its mission. The first was a mission with a reasonable number of waypoints, one POI and the curve size set to 1/2 the distance between waypoints which results in a perfectly smooth circle:
As you might have guessed, this did not result an a smooth yaw movement.
Next, I tried a similar mission with many waypoints. I got the same result:
Third, I removing the curved turns, using straight paths between each waypoint. Unfortunately, I experienced the same result.
All missions were flown at a slow 5 mph. If there is a way to smooth the yaw movement, I have not yet found it.
Again, with my M2Z (on-board waypoints), the yaw movement is perfectly smooth.