Poor D.C. United. US Open Cup success aside, it’s been about as frustrating a season as a team could have. The first few months were filled with growing pains, trying to find a way to mold the side around new Argentinian signing Marcelo Gallardo. It began to pay off in early summer, with the team finally finding form and playing with the easy-on-the-eyes attacking style in such a marked contrast to some of the league’s…