For me, SwiftUI does exactly two things better than UIKit: tables and collection views. For everything else, it's so much easier to get stuff done with UIKit*, regardless of if I'm working with Interface Builder or making UI in code (as per various projects I've dropped into).
In theory, reactive UI is good. In practice, at least in the case of SwiftUI, the "magic" data passing does sometimes fail — perhaps someone put in the wrong @ on the property — and then you've got to debug some weird magic, and if there's a sensible place to put a breakpoint for that kind of problem I have yet to learn it.
In theory, the UI is reusable across all Apple platforms. In practice, the nature of the user experience is so different that actually trying this makes it suck for everyone — you don't want finger-sized buttons on a mouse-driven UI or tiny mouse-suitable click areas for a mobile UI, and I have no idea what the user expectations are for tvOS or WatchOS despite having written apps for both because hardly anyone shares their experiences and lessons learned.
In theory, having the code be the source of truth for the WYSIWYG editor is great. In practice, the WYSIWYG editor keeps giving up because of e.g. a compiler error, and decides to stop forever until you manually resume the preview.
* I'm mostly on iOS rather than macOS, but I'd assume UIKit and AppKit have the same strengths and weaknesses.
