You're not getting it. That was done with an iPhone 6s NOT the Plus! The 6s has no stabilisation.
Incorrect, watch it again.
The camera in the iPhone is impressive, but it is not meant to replace action cams, nor is it ever going to be as smooth as a GoPro on a gimbal.
Nor is a phone meant to be mounted anywhere on the exterior of a car. I don't seem to understand your point. Are you saying iPhones will make GoPros obsolete? They won't.