Someone should assemble a chain of iPhone camera review comparison images published over the years, 18 → 17, 17 → 16, 16 → 15 etc. showing how each year's new phone being so much better than the previous year's somehow becomes perceivably bad next to the next year's phone.
I'd suspect the average person won't notice much difference (on the main lens) until about iPhone 11 or older, with still photos. Computational image processing does a TON of heavy lifting with these tiny sensors.
With video OTOH, the improvements are much more noticeable. I also suspect that is why Apple focuses so much on video as its a harder problem to solve and so much easier to differentiate your hardware from competitors.
Could you provide at least one review to support that claim?
Youtuber Marques Brownlee did this (as a short). It's actually not so noticeable, it's only once you get to the very oldest phones that it's visibly worse.
the difference will be in things like low-light, telephoto lenses, video capability, HDR, and lots of other things that don't show up in most photos (including that one)
https://www.youtube.com/watch?v=jru9Gsz3kJY