I spent some time with Swift-on-the-server last year and definitely felt like the class/struct difference made sense.

But I have to agree, from a novice eye at least, result builders look to be a feature added to support SwiftUI and limited other use cases. Have you seen many examples of third party libraries successfully using them?

And while we're here, do the introduction of macros in Swift 5.9 allow room for replacing result builders with something more uniformly useful?