The performance is bad; the developer experience is bad (it's a moving target, not a stable point); it was done to chase a trend (reactive) and to boost other Apple platforms (macOS, watchOS, tvOS, and now visionOS) rather than because it was the right technical solution; the UI and UX it generates is poor; and Apple (but not only Apple) seems to have stopped caring about quality over the last few years.
(On that last point, I decided to skip macOS 26 because of all the issues, but here's what I faced with their -2025 offerings: https://benwheatley.github.io/blog/2025/06/19-15.56.44.html)