I would love to take a few people who claim to notice the speed differences and have them do the Pepsi Challenge to prove it. Get iPhones from the past 8 years, put them in big cases that only show the display and hide which vintage they are, and ask people to see if they can guess which phone is which, or rank them in order by year. I bet most people, including the self-professed experts, can't.
The 120 Hz displays are very noticeable when side-by-side. For example, my iPhone switches to 60 Hz on low power mode and it suddenly feels like it's a fast slideshow instead of "smooth".
There is also an adaptation factor: Good performance is only noticeable in contrast to poor performance. You get used to it very fast and stop noticing, unless you go back to the old system which suddenly feels "broken", even though you may have considered it perfectly acceptable before.
