As a stills only photographer, who uses both, P4 Pro and MPP, the cameras on both have limits. I have attached a 3 shot Vertical pano from the P4.
The Mavic, as the OP has shown at ISO 1200, may not be worth the shot, too much noise and loss of details, even in raw. I don't shoot my MPP past ISO 400 and that is rare. Net, it's not a low light camera. You can gain some advantages by:
1. shooting in AEB 5 shot, you have a -1.34 to +1.34 range. Yes, odds are you will be throwing away files, but attempting to dial in correct exposure on one shot is just to hard.
2. Shot in raw, (which you are doing)
3. Shoot only up to ISO 400, and try to stay at 100.
4. Use Tripod mode and go longer exposures. If you don't have a lot of wind, you may be pleasantly surprised with results.
5. Make sure to focus the camera using AF, (I realize hard to do at night may be impossible) then switch to MF. But manually focusing a drone IMO is not possible with an iPad as the resolution won't allow it. CS is a bit better, but still hit and miss. AF works very well.
6. The Mavic sensor allows for a bit of pull down on highlights, but very limited push in shadows. So allow for your sky to go to the right on the histogram, in raw you will be impressed with how much you can recover.
7. Capture One does a better job on the images for noise IMO, LR has a much better lens profile. C1 you will need a LCC.
8. Mavic lens is very prone to flare, horrible flare especially if the sun is coming from an angle. Lens hoods work great, but you can't fly fast or do a 9 shot pano as the hood shows.
As to the P4 camera,
Yes, it's better, 20MP and larger imaging area. I find it also suffers from noise and retro focus distortion may be a tad worse than the mavic. You can't rotate the sensor to portrait mode as the Mavic can, so when working a pano, you are stuck to only landscape orientation and that makes the distortion towards the edges worse. Tripod mode also helps with the P4, maybe more so than the Mavic.
Noise, I agree it's better, but not what I had hoped for. I also find that the blues seem to have very little room left (LR/ACR), where as the greens have a ton of room. Pure blue sky is hard to get right. The shadows have more range at ISO 100, but again past 400 and things get ugly.
Shutter, you have a mechanical shutter, huge advantage for sure, and you can select a wide range of aperture, however much past F 6.3 and diffraction will start to show up.
Lens, overall OK, but just like Mavic, hard to get right all the time. I often focus recompose a lot as many times the first AF/MF setup will not have the corners, one will tend to be off. However I have also gotten some excellent details from the camera when I happen to get the focus right. Again, manual focus is there, but IMO way to hard to pin point. The touch AF (like on the iPhone) works pretty well. Adding a polarizer/ND will cause you to miss sometimes however.
LR IMO does not have as good a lens profile as they do for the Mavic, and I use the one for the Inspire 1.
I often see a tiny hard vignetting towards the edges of the top of the frame.
I quickly gave up on the 9 shot pano with the Phantom, as the props show on the top frame every time. Props showing in flight are also a bit more problematic for me.
Between the two, color/contrast/saturation are very similar both are Sony chips.
Single biggest issue with the P4 ITS LOUD, you can hear it 2000 feet out, so I tend to only fly in remote locations. It just makes a lot of noise. 2nd biggest issue SIZE, it's huge and can't be broken down.
I love the MPP for both it's size and portability as I can carry it, controller, 4 batteries and my DSLR with no problems. Not true with the P4, it needs an entire pack just for it. At 200 feet up and 500 feet out, you have to strain to hear it also.
Dream machine is the Mavic with 20MP but that appears not to be in the cards. Latest P4 Pro V2.0 doesn't seem much quieter than current P4 Pro.
I have not shot any night work with either drone, did a bit with my Spark and quickly moved on. From previous posts, the P4 obviously can do a good job.
Paul Caldwell