Okay, but did you attack that problem in a way that actually is more efficient than established UI paradigms?
Let's split the problem in two parts:
- "Semantic" Design (Checkbox, ImageView, TextInput...)
- Visual Design (fonts, colors, margins, ratios)
Your solution covers only the "semantic" part. Just look at the data. It's basically a simple component tree. It would be more efficient to just type it up. It also would be more efficient to just drag rectangles from a toolshelf instead of defining the type of the rectangle by drawing extra hints.
As for the visual design, that's where you use a design tool like Illustrator or Photoshop. Typing that up (e.g. in CSS) is surely a pain, but sketching it all up is out of the question. I certainly do see room for improvement in the workflow here, but a sketchy interface isn't helping.
You have to question a lot of assumptions here, but also consider how designers are most efficient with the tools they already know and have used for years. Don't mistake something that you want to create for something that users will actually want to use.