This was a surprise to me. I always thought Apple engineers worked on the next flagship device and the lag on older hardware was because they didn't optimize iO

This was a surprise to me. I always thought Apple engineers worked on the next flagship device and the lag on older hardware was because they didn't optimize iOS for the older devices. As an app developer myself I tend to test my app on the latest device that I could get hold of and the older devices are an after thought (most of the time).