This is because GPS altitude is based on an ellipsoidal approximation of the earth's surface. As you have found it can differ 100s of meters from actual altitude and is not useful for the altitudes typically flown with drones.
I doubt there's another country in the civilised world where the term mainstream media is used as a pejorative.
Whenever you see that term being used disparagingly, you can tell a lot about the person using it.
More than five million people participated in protests in the United States on the day of the birthday parade. There were essentially no problems. The events were peaceful. No innocent citizens were blocked. No looting. No police cars set on...