Not knowing the technology baked into the new iPhones, I am surprised at how well it does. Okay, not really. I suppose impressed is a better word. I know Apple spends a lot of time and money perfecting their products.
For the GoPro, there is software out for FPV drone guys called Rock Steady which reads the motion data ahead of the image (something that can't be done while recording) and then adjusts the image to where it knows the movement will be, even further stabilizing a fairly stable image. It's pretty cool, but have no idea if it works for the slower movements here. I would be curious what the outcome is if post-production stabilization software were applied here. (Does anyone do that for vlogging?)
@Chris I too have a DJI gimbal for my phone and agree that it's a bit large and difficult to control, but on a tri-pod with programmed movements, or fairly slow and long pans, I don't know of anything better.