I absolutely agree with everything you say, but you have to realize something:The strategy is working for Apple.
Planned Obsolescence do exists, there's much evidence to support it. But who are the ones that are always denying that? Who are the ones that are always bashing those who complain about the problem?
I'll tell you exactly who:
iPhone 6S Plus 128GB <Bought on launch day> = Most people with the latest devices.]
Those who practically bash the previous iPhone model the day the newest goes on sale. Those who are CAMPING outside Apple Stores before the new iphone is EVEN ANNOUNCED!
People whose preference is so obsessive over Apple that their sympathy regarding other users is limited to this:if you don't buy the latest model then go suffer in silence.
Yet most of them dare to comment on the matter with no info or facts but sarcasm or name-calling.
That's the proof that it's working perfectly as intended.
Needless to say, not every Apple user is like that. There are those who love to get the newest devcies as soon as possible but are perfectly aware of problems with the older ones.
Then there's the "Switch to Android" kind.
Apple is in the business of selling the latest hardware and software. Software is optimized to the latest hardware. You have older hardware? Tough luck. Wait for the iOS updated to have it optimized to your hardware. That is the way Apple has been working since iOS 7. This is the new pattern. We have seen it with three iOSes so far.
Knowing this, you have options. First, stop buying iOS devices. Vote with your wallet. Second, accept the above fact and wait until your device is optimized. Usually by the second or third major update your device will be optimized to the iOS. If it is not, well, sell your device and get an Android or Windows phone.