more by accident than by design

more by accident than (by) design -- нечаянно, ненарочно, по случайности; без злого умысла

whether by accident or design

The pilot, whether by accident or design(=whether it was planned or not planned), made the plane do a sharp turn.

However, it's pretty evident that 'more by accident than (by) design' differs from mere 'by accident'. Who could explain the difference?