https://techcrunch.com/2017/10/06/benchmarks-contradict-apple-slowed-down-my-iphone-claims/

It’s a refrain we all hear every year around September: “I swear, whenever they release a new iPhone, Apple makes all the old ones run worse to make you upgrade.” But thousands of performance tests conducted over the years by Futuremark users show that the conspiracy is mostly in your mind.

If you don’t know Futuremark, it’s the company behind the benchmark software 3DMark (among others), which for years has been a standby for testing how devices from gaming PCs to phones perform.