You can fuck up good sensor data in post-processing. I find the iPhone 6 and iPhone SE cameras to have too much noise reduction (or maybe JPEG compression) applied. Even in daylight, the images are very soft.
I'm not expecting D810 quality, but I do find it suspect when artifacts appear in blue skies. There is plenty of light, there shouldn't be any noise. Then again, there are a lot of pixels packed into a very small space.