Optically very similar, at least for stills. The P4 Pro has a mechanical shutter, M Pro 2 only e shutter. Both are 20MP, I believe both are using the same Sony 1" sensor similar to chip Sony uses in RX100.
P4 Pro has a few more crop modes, 4:3 for example.
Mavic offers a few newer active track modes just like mavic air.
I have used both and for stills work the cameras are very close. The Mavic Pro seems to have just a bit more DR and highlight recovery, at least from the few flights I have made with it compared to the P4 Pro.
Im editing a VERY eye-opening video right now that has side by side tests that also include resolution charts. Just a hint....the differences in clarity and resolving power are pretty drastic. Another hint.....Mavic-II pro's 2.k mode offeres the EXACT same resolution as its "4k" FOV full wide mode. There is allot Im covering on this. Will be out on a few days.