Funny. Apple introduces a new iOS version and instead of it adding new features, you’re forced to relinquish a number of them to make the device perform as well as it was running on older iOS. Brilliant! There's an article on Redmond Pie (Myth Debunked: Benchmarks Show Apple Isn’t Deliberately Slowing Down Older iPhones With New iOS Releases). However, the test did not take into account the performance (or lack of) in opening and switching between apps, activities that you normally do countless of times on a mobile device.