What is the handle of a section’s default entry type? For a section without additional entry types, what would be the handle value of the default entry type output by {{ entry.type }}?
The default entry type created for a Section (all types) gets the same name and handle as the Section itself.

You can change the default entry type's name and/or handle by visiting Settings -> Sections, clicking on "Edit Entry Types" next to the appropriate Section, and finally by clicking the relevant entry type's name.