Yea I just swapped my jogging/beach iPhone from an Xr to an iPhone 12 and wow, it's so much better than the Xr and pretty much as good as my "proper" phone, an 17Pro. It's got 4G RAM instead of 12G but it performs almost as well. Xr->12 is a huge leap in performance and I noticed it straight away. But the 12 against the 17 is much harder to see the difference. Less redraw of icons on the main screen is the primary thing I've noticed.

The only noticeable thing is faster screen, the 17 has 120hz screen.

my eyes are an older model

The difference is noticeable even if you pretend to not notice it for cool internet points. ;)

I can definitely spot the difference. But I don’t think I really care. If my MacBook mysteriously swapped from 120hz to 60hz, it would probably take me several weeks to notice.

I'm still on an iPhone 11 that I bought second-hand a few years ago when the iPhone 15 was the newest. The battery life isn't great which is the only thing tempting me to upgrade, but I'll still put that off as long as possible.

Other than the battery I have no complaints. It's a phone. I can make calls, send texts, browse the web, check maps, take photos. What more do I need? Why waste money?

I can't even tell the difference between newer iPhone models. Why do people upgrade every year? What's the point?