Upgraded my wife's phone from a iPhone 7 to XS 256. Frankly what struck me the most (as it has on the Android side as well) is how little difference new phones make in day to day use. Yes you get some more screen real estate and the camera is better, but you don't notice the performance in normal use and ultimately you're still surfing the same sites, messaging in the same apps, etc. The plateau IMO is real and I'd actually recommend the XR to most people now.
Oddly enough, the XS felt weirdly similar to my S9+, though obviously smaller. It felt dense (unlike the metal iPhones which now feel ridiculously light), it's all screen and glass, the cameras are more alike than ever before, and you use the same apps on either device.
I honestly don't understand folks who are die hard in either camps - I can switch between either phone and if not for the different gestures, my experience is almost identical.