To nip this one in the bud: Atlas doesn't generate code. It serializes the objects that represent the "views" and other objects. This has a number of advantages over the code generation method.

Also, I think Atlas allows for the sort of abstractions you're looking for. It comes with a bunch of built in widgets which are great, certainly for prototypes and simple UIs, but even fairly advanced ones too. But if they're not good enough, or you have some custom widget/layout you can easily add it to Atlas as a plugin and treat it as if it were a built in component.

But I'm certainly interested in hearing more about the problems people have with these sort of tools.