I remember Apple promising better performance and responsiveness with iOS9, it was in their marketing materials, and it turned out to be a complete disaster with multiple lawsuits accusing Apple of rendering iPhone 4 unusable. That was the only time I can remember Apple explicitly marketing better performance on a new iOS release in the last 10 years and it actually delivered the opposite.
So I'm excited and all to see reports of the iOS12 beta showing better performance, but before we make grand statements lets remember we've had a clear pattern over the last 10 years of slowness, keyboard hiccups, stuttering, etc etc on each iOS release. Whether it's intentional neglect or not, it's extremely convenient to say the least that each iOS release for the last 10 years has been bogging down iPhones.
But it's more convenient that Apple only gives you 2-4 weeks to downgrade, and then exiles you from doing so. Why not give you a few months? Security concerns? Really? It was announced only 80% are using iOS11, what about the other 20%? 20% represents MILLIONS of users supposedly with disastrous unsecured iOS10 or earlier. It's armageddon right? Please.
iOS 12 might deliver on the promise of better performance. That's one iOS release in 10 years that might reverse a trend. But what's going to happen in iOS13? Do you see Apple really going out of their way to optimize old hardware? I don't, we have 10 years of evidence, Apple generally doesn't care.
If there is no conspiracy then allow users to downgrade, because I guarantee you that either iOS13, 14, 15 will bog down iPhones and we'll be back on the same boat.