If the sudden yaw motion is the main objection, then reducing Stabilization->Advanced->RateModeResponse(yaw) or MaxRateLimit(yaw) would slow it down.
If you can accept the general flight corrections and response being slower you can adjust this for roll (and pitch) as well. Slowing these down way way too much might require changing the VtolPF PIDs though.
You could also try changing the System->Settings->VtolPF->YawControl to MovementDirection, but be aware that this setting can cause problems in other GPS modes like VelocityRoam (at least in earlier versions) when you are motionless, if your yaw rate is high enough. When motionless, it randomly yaws all over the place. ... The reason this should help the yaw motion is that even with a sudden bank sideways, the sideways velocity does not jump but changes smoothly. Like pressing the accelerator pedal in a car. The velocity does not jump to 70, but increases smoothly to 70.
Of course you can also set YawControl to Manual, in which case yaw doesn't move at all unless you move it. This can work well if you are watching via FPV and yaw it around slowly when you see it bank.
You didn't mention whether you were doing video and have a 2D gimbal. If you do, fixing yaw rate should be enough.
There is another setting that I have not played with that might help too. System->Settings->VtolPF->CourseFeedForward. You might try increasing this a bit, but if you don't see improvement with it set even as high as 5, I would set it back to default. I would guess that this should be kept below the length of time between your waypoints?
Finally, there is (or at least was) a way to program a part of a circle into the waypoints, but I haven't used it. I recall @f5soh tested it a long time ago. You fly to a waypoint and when you get there, you don't go to next waypoint, you do a part of a circle, and when done with that, you go to next waypoint? I am guessing you should use YawControl=MovementDirection with this.