I am still leaning towards incompetence to get certain devices right. I mean i can understand that there are a lot of difficulties to get slow A5 devices to a very fluid state while maintaining features and security. From a technological standpoint they probably should have been cut of by now with some sort of last special optimized iOS (maybe with the option of security patches).
But even more concerning is the state of A7 iPads. Looking at the performance difference between A5 and A7, i am wondering why those iPads seem to age even worse than the iPad 2. Don't get me wrong, even "high end" games perform still reasonably well on them, but the UI performance (without reduce motion/transparency) is really below Apple's standards.
Why do they let this happen? An intentional slowdown makes no sense, because Apple is still selling the rMini 2/Air. If they think there is a market for those devices, why sell it with underperforming UI? Touch ID,better cameras, good screen quality, weight etc. should be enough to differentiate them from the rest of the lineup. I never heard of any upsell marketing strategy, where you cripple your own product in such a way. Either they are evil geniuses of they just have a problem with their software quality management/resources.