I hope this doesn't stray too much into Austenuations, but you've just made me realize that this is parallel to the description of Catherine Morland at the beginning of NA, and how we learn what she's like by hearing all about what she isn't. According to Marianne, Edward Ferrars is not passionate, dashing or impetuous enough, so we are to deduce his true nature from all of those "deficiencies" (as Marianne sees them).