They have same sensor size. The difference is the focusing system. The P3A has fixed infinite focus which is perfect for aerial work. The Mavic has variable focus and has caused user error issues from the start. Prior to the launch of the mavic, I recall Vlogger Casey nutsack (sp?) was disappointed with the images because he didn't read the manual about tap to focus. This has been rectified now as the Mavic has AF-C and AF-S modes which kinder corrects the focus if you forget to tap the screen.
Another issue with the Mavic is the noise reduction used in sharpening. If sharp = 0, then trees/grass looked water painted. The fix is to set +1 for sharpness.
And finally (slightly off topic), is the video recordings at frames higher than 30fps. 50/60/96 fps looks rubbish. Its all pixelated and a moire effect is created when you film objects with parallel lines like corrugated roofs etc. This is to do with the limitation in the hardware of the camera and i believed its resolved now with the upgraded platinum mavic pro.
The Mavic is a perfect system if you overcome and understand the limitations. I would take the Mavic all day over any other drone.