First I've read this.
Your 13mp statement sounds authoritative.
Where does it say that in manual or elsewhere?
If true, how can DJI advertise it as true 20mp?
As to lens vs. camera, having gone through (4)
P4P+ camera-lens replacements (covered by warranty),
it seems off-centeredness or similar causes vast variations
in quality of
P4P+ image IQ. I've had (2) in which
diffraction issues caused blurriness starting just outside
center of image, whereas (2) others were sharp nearly
to all edges.
Summarizing: a lemon** better lens does not beat
a good worse lens!
And my small sample of (4) lenses implies a lot of
P4P owners don't know they have lemon lenses...