They are probably taken with the inbuilt camera app and are compressed jpegs, straight from camera. When the 8 plus, I can only talk about that, as it's what I have, is used with a third party camera app and the images are saved as RAW files, it's very good for a sensor that's less than a third of an inch square.
I think a lot of it comes down to peoples techniques. Some people are as wobbly as, when they hit that shutter button on the screen so hard. The third party app I use, I have set up to take an image when I remove my finger from the screen after locking focus and exposure.
You could always go one further and work from a tripod, using your headphones and triggering the shutter with the volume up button for the absolute best stability possible. Quite a few famous mobile phone photographers do this all the time.
You’re probably right.