This is just how DJI is handling the Shutter Priority internally now. The P3P and the P4P are getting the same setup but the different models are handling differently since the P4P is fancy and has a adjustable aperture.
The reported motion blur is calculated by multiplying the aircraft speed by the exposure time which gives the smear distance. 1 cm of ground smear isn't usually an issue but that doesn't mean it was in focus...
The problem with adjusting the aperture to address the incoming light is that it changes the composition of the image. The autofocus is pulled when the aircraft reaches the cruising altitude while the aperture is at some value but then as the lighting changes the focus may change a bit, especially if you are flying low or the terrain is rolling.
Short story: we don't have any control over how the camera does it's shutter priority adjustments.
