Ehm, the problem is actually the opposite, I know very well how OS’s and software works - It’s my job, and has been for 30 years. And while I'd love to say you are right it’s just more complicated than that. Of course new features, API’s and functions requires more ressources, and as such one can resonably expect slower performance with each new major release. The problem is that the software written today - is created in VERY inefficient high level code and after compiling it, it uses absurd amounts of ressources compared to what it could be using, if written 100% optimally. I'd wager that if IOS12 and apps was written 100% optimally it would probably be at generally 3 - 5 times faster and probably use about one fifth of the memory. The problem is that writing it like this (and in machinelevel code for 100% optimization) would be impossible. It would probably require a hundred or a thousand times more manpower, and would never reach the marked in a timely fashion. So what they do is make a tradeoff that's also very good for business. They optimize very little which speeds up development but unfortunately requires you to buy a phone every 2 or 3 years to have good performance due to added software bloat.
The major gripe with this approach is that today we are at a point where optimizations to make the OS runs VERY good on fx. iphone 6 and 6s would be comparatively easy, but the business incentive is not there - so it's not being done. We are actually so far down the "bloat" code path now that it's being used actively in "slowing down" older devices to make you purchase a new device (planned obsolecense).
What we need is a little more environmental responsibility from these manufactureres so we do not use up all of earths ressources to produce new phones and computers to run new and higher level code, but instead use the hardware already produced much more efficiently. But there is no money and business to made from doing that...... So we just continue doing what we always did and destroy the earth to make the top 1% people even more insanely rich
Just to make one thing clear - this is VERY far from apple fault alone - actually the OS is by far the most optimized codestack on your phone. The problem is very much with the app developers as well as they use insane amounts of memory in inefficient code and that forces the OS to start making "unhealthy" performance decisions to free up memory. Probably the best example I have seen on this issue is the Slack client for Windows. It's a simple chat/notification client, but it easily uses 800Mb to 1Gb+ memory to startup. If written properly and optimized I'd wager it could work perfectly with less than 20MB of memory. That's a 40 to 50x bloat on ressources just because they can reuse code across platforms and spare expenses on optimizing the code.
