Your NSA quote is a little out of context. The article you link to states that German is the fourth-hardest language from a list of five comparatively easy languages.
> Among Vietnamese, German, French, Italian and Spanish, Vietnamese may be the most difficult... Next to Vietnamese, German may be the most difficult
This doesn't amount to being significantly harder, particularly in light of the statement (that you quoted) that there is just one feature that makes it harder than the other three.
Speaking from personal experience (native English speaker, no prior difference in exposure to the two languages, simultaneous study of the two, similar teacher quality and curriculum), I found French harder than German. Although my single anecdote doesn't prove German to be easier, surely it suggests that the one I found easier couldn't be significantly harder.
> Among Vietnamese, German, French, Italian and Spanish, Vietnamese may be the most difficult... Next to Vietnamese, German may be the most difficult
This doesn't amount to being significantly harder, particularly in light of the statement (that you quoted) that there is just one feature that makes it harder than the other three.
Speaking from personal experience (native English speaker, no prior difference in exposure to the two languages, simultaneous study of the two, similar teacher quality and curriculum), I found French harder than German. Although my single anecdote doesn't prove German to be easier, surely it suggests that the one I found easier couldn't be significantly harder.