How did you do the conversion from your example Taskpaper file to OmniFocus? I tried using the Editorial workflow and what I get are 3 projects (named Folder A, Folder B, and Folder C) with Sub-projects nested into them - but no folders.
The second issue I mentioned is that I cannot find a way that would allow me to select a folder in OmniFocus (e.g. Folder B) and copy it and its underlying structure with the subfolder and the Deeper Project project as a Taskpaper file - there is no share button which is the way I would do it if I wanted to copy a project.