Try not to worry too much about getting a perfect lens (all the
sensors are fine - the lens is the issue if you are seeing uneven sharpness - seems to be some confusion there). You'd know if you had a bad sensor - usually that manifests itself with entire lines of dead/stuck pixels or green/red lines, or it simply doesn't work.
I have $3,000 DSLR lenses that show more variation than some of these
M2P tests and it is for the most part completely normal. A small amount of lens decentering is considered normal even in very high end lenses, which will create small sharpness variances in different parts of the frame when you shoot a test scene or chart and scrutinize at 100% (usually corners). If it's severe or very central, obviously that is a warranty issue that needs to be dealt with, but if it's only minor, you may very well find your replacement is worse.
Lenses will almost always be sharpest in the center, and that will diminish as you get to the edges/corners - this is true even of some of the best optics money can buy. Stopping down will reduce overall sharpenss after a certain point, but increase corner/edge sharpness because you are using a more central portion of the lens. In the case of the
M2P though, after F4 diffraction starts to degrade the image and quite noticeably so beyond F5.6. F8-F11 are unusably bad outside of emergencies, in my opinion.
Most lens issues are also magnified at close subject distances one might use for testing, but are the opposite of how most people use their drones 50-300ft in the air or whatever. Make sure it actually impacts your field usage before opting to roll the dice on a replacement.
The reason you might see some areas of the image sharper than others when using different focus points with the camera otherwise stationary is due to field curvature and many lenses are affected by this to some degree, especially wide aperture wide angle lenses like the one on the
M2P. Again shooting at relatively short subject distances at the widest aperture will exaggerate this phenomenon. Curved lenses naturally want to make a curved image, but the sensor in the drone is of course flat. When a lens exhibits field curvature it may be focused, say, 10 feet away in the center of the image, but the focus would only be 7 feet away at the mid part of the image and 6 feet away at the edges. Again, perfectly normal if you need to shoot test scenes and view at 100% to easily see it. Way up in the air this would be covered by the enormous DOF of the tiny 1" sensor and shouldn't be visible.
For general usage, the DOF on the
M2P is so enormous (basically from about 3 feet to infinity once you're in the air), I haven't changed my manually set focus setting since I bought my drone. I keep focus peaking on as a confirmation but haven't had to adjust it yet. If your subject is very close you may need to adjust that, and I never recommend using autofocus as it can very easily ruin your footage if it hunts even a tiny bit, especially if you don't notice until you get home which is likely.
My advice is if you need to pixel peep test charts are relatively close distances to notice anything, your drone is fine. If you are performing a test that will coax out phenomenons like field curvature, your drone is fine. If you can see obvious and distracting softness in unnatural portions of the image (i.e. not near the edges/corners) that are visible during normal viewing/usage, then I would consider a replacement.