XAML is the only thing I was ever able to write a complex layout in, run the app, and see it look exactly as what I intended on the first attempt. That would meet my definition of productivity.

For example, my experience with CSS has been the opposite of that. F5 a million times before the layout works the way I want it to. Sometimes even googling how to do create some type of layout because I can't think of it on my own.