GPS Elevation Accuracy Test: Smartphone Apps vs. Dedicated GPS -
"Hardware
Many high-end GPS units feature a barometric altimeter in an effort to improve elevation accuracy, but truthfully it doesn’t make much difference. As one GPS company rep confirmed, a barometric altimeter is pretty useless unless it’s regularly calibrated. That’s because it uses atmospheric pressure to determine your altitude–but atmospheric pressure changes not just with elevation, but also with the weather. Only one of the top 4 units listed above features a barometric altimeter. The worst-performing unit includes a barometric altimeter as well. And FYI, our test happened a few hours after a massive storm system rolled through."
while I dont remember the exact model number, being a few years old, I can tell you it was a 59 dollars special, not a high end one. But even the "high end" GPS units use GPS with baro assist only. But again its irrelevant, because unless you have an aircraft grade pitot tube fed barometric system, they are not accurate enough to determine altitude alone, as was repeated by the GPS company rep above.
Im not understanding why your so deadset in proving your point on this? The reason I say I know for a fact the Mavic does, is 1. why have it available to the unit to record elevation for pictures, but it not be used for the unit? that's just stupid. 2. During one of my phantom (not Mavic, but why would the system be different in how they measure systems, becuase they both use DJI4 it has to read the same sensors and settings) repairs, I broke the barometric daughter board by accident, and GPS readings were still available. 3. GPS is more accurate.