Rewriting an app from UIKit to SwiftUI not only eliminates storyboards but also reduces the code base. So once again: you have code plus storyboard XML vs. just code that is smaller! My jaw dropped when I first discovered this while rewriting something.
Unfortunately though SwiftUI hasn't completely matured yet. Especially if you are targeting iOS versions prior to 16, you will encounter many of SwiftUI's shortcomings. Some (many?) UI components are still UIKit under the hood, scroll view and its derivatives are still not as flexible as you sometimes want them to be etc. For some custom UI tricks that would be a piece of cake in UIKit are impossible in SwiftUI and you often resort to wrapping the old components in your custom ones.
Oh and don't get me started on resorting to the main thread (because of the underlying UIKit code) in the age of structured concurrency.
All in all, the concept of SwiftUI coupled with structured concurrency is beyond amazing but its maturing process is still underway.
I'd been out of iOS dev for a good long while, and was still thinking in UIKit and Obj-C.
Overall I've found SwiftUI to be the most productive and enjoyable declarative framework and developer experience I've used!
To be fair my experience is limited to React and Flutter, but still, Apple have done a rather excellent job IMHO!
YMMV :-)