Lots of great and specific points in these threads, many of which I have personally seen.
SwiftUI was really promising at first, and even fun to use (nothing like ripping out entire UI files or pages of code). Yet, issues were almost immediately apparent.
A major concern is that it seems to take Apple a really long time to address even basic issues, e.g. years go by and things still broken since day 1 are there, while other things are randomly introduced. And of course, “Feedbacks” have the usual dice-roll effect: will you even get a response, much less see any indication that the reported bug will ever be fixed? (Or will Apple just wait 2 years, close your bug as “probably fixed in this OS update, please confirm”, and repeat the whole thing?)
And the thing is, this is not hard to believe. If you auto-complete in SwiftUI (what else can you do, there is rarely good documentation?), some of the APIs are truly scary: levels of complexity and variation that really make me wonder if they can truly test, much less support, every variation of every API. I would strongly argue that some things just have way too many options instead of a handful of clear starting points.
SwiftUI also occasionally changes behaviors (e.g. subtle or gross layout differences). Worse, it is easy for Apple to not call any of these changes “breaking” because apparently you are just supposed to let SwiftUI figure out what is needed in any situation. Except that kind of “trust us, we’ll come up with something” approach is not great for writing stable production software.
The auto-generated hierarchies can do truly weird things. For example I realized at one point that an “auto-saved” window layout auto-generated preference names based not on a simple string but the entire SwiftUI view hierarchy, which was huge and indecipherable and of course would become a different value if any part of the window or view hierarchy was modified. So I discovered I had dozens of preference settings scattered throughout my defaults, 99% of which were completely obsolete because they were based on previous incarnations of the view I was developing, and they all had names that were almost impossible to type (so how do I delete them while preserving the rest?). What do you even do with that?
Yet another major concern is that SwiftUI is very dependent on Combine which is not necessarily the future given other developments in the Swift language. So what if they just decide to, say, deprecate Combine and move further toward actors and async APIs? How much of SwiftUI might just fundamentally change in, say, WWDC this year, completely invalidating years of effort people have put into it?