The Design of Everyday Things should be required reading for Apple's UX designers. This used to be a book that informed the core of their design philosophy. Unfortunately, that seems long gone.
If a user can't figure out how to do something, the user is not to blame. The designer is. With so many features in iOS now completely invisible to the naked eye, it's very clear who is responsible for this mess. And it ain't the users.
I don't think it's a failure of design, but rather a symptom of too much functionality.
The original iPhone had ~30 features it had to make work in harmony with each other. The current version of iOS has thousands. Each additional feature is an increase in difficulty in making it feel harmonious, and it's beyond the remit of what a single designer with a single vision can handle. It's grown to a scope such that no single person can contain a mental map of every aspect of it at once.
Gotta strongly disagree on this. For example, I know there's a way to get to the app switching screen, which shows all of the apps in a grid. You just have to drag up from the bottom the right amount in order to get the grid to stay. Despite knowing this, I fail to do it half the times I try. I just can't figure out how much to "drag" up from the bottom. Too much or too little and it just doesn't work. So frustrating. And so many other similar examples.
In this case there is both time a distance limit to the gesture. If the gesture is too fast the switcher won’t appear even if the distance was long enough.
That said, personally I’ve always found the gesture navigation very intuitive.
If a user can't figure out how to do something, the user is not to blame. The designer is. With so many features in iOS now completely invisible to the naked eye, it's very clear who is responsible for this mess. And it ain't the users.