Re: Happiness, my personal experience corroborates, for what it's worth - though inversely to the headline: I love iOS development and can produce reliable, complex UIs with react-ish state-view management in a day, with no 3rd party frameworks; when I do web (UI mostly), I'm miserable and unmotivated.
I've been lucky enough not to run into the things people often complain about with Apple. They don't mysteriously reject my apps; and when they deprecate/require something, the reason makes sense to me and it's easy to accommodate. The differences I experience are rather in the quality of languages and APIs/frameworks.
SwiftUI is the exception. If they deprecate UIKit/autolayout, I'll move to the backend in one weekend.
Probably significant in terms of speed of development, time spent maintenance projects, etc