My experience with the iPhone camera (X) is that smudge artifacts (AI, compression) are quite noticeable even on the device's screen. As soon as you put that on your 30" desktop monitor, the photo is nearly unviewable. This hasn't been my experience with mirrorless cameras, whose output looks pretty good at 1:1 on a 100dpi screen.

There are two photographs that come to mind where the iPhone utterly disappointed me. One was a morning park scene, rays of light filtering through leaves. The leaves just looks liked blobs. Another was on a boat at night; with my eyes I could clearly see texture in the buildings on the illuminated skyline, reflections on the water, and texture in the water. The iPhone shot was just a black screen with some blurred specks of light.

I know I could have gotten both of those photographs with my A7ii. I have handheld nighttime pictures with stars in the sky. A big sensor gathers a lot of light, and even more important than getting close is collecting as much light as you can.

I meant, when you open the image at its true resolution on a computer. But I agree that prime lenses are close to always better in quality than variable length ones, even if for some situations you need a telephoto anyway (and having a fixed 300mm in my pocket does not seem practical).