Well, what's happening to my phone is that every few seconds screen blanks out, running apps crash and the phone goes back to the lock screen. The battery is also draining fast and the phone is warm to the touch.
Not everything has to have a malicious explanation.
I doubt Apple is deliberately adding bloat to iOS, but every major version is definitely heavier than the previous one.
This argument doesn't make sense from a logical point of view. If all iPhones eventually crawl to a halt because Apple ruins them with software updates, why would that push people to go buy a new iPhone? Wouldn't they look elsewhere?