[koffiezet]

In my experience with iPhones, this was true for older generations where they simply didn't have the processing power for newer OS features. My switch from my iPhone 4 to a 5 was strictly for performance reasons, but I went from my 5 to a 6S just to have something newer with mostly a better camera and touch-id. Performance-wise the phone was still perfectly usable (my brother still uses it). Sure it was a lot faster, and there still are massive leaps in performance with every generation, but these days that performance is mostly used to race to idle for improved battery life.

For the current applications, an iPhone 5S level of performance - a phone which is 4 years old - is still very usable today. That's also why Android flagship phones aren't really in trouble while still struggling to match the performance of a year-old iPhone 6S, and can't even dream of getting near the iPhone 7's performance. They mostly try to compete with stuff people do notice these days: the camera - where they have a lot more success.