I don't mind this at all! In fact, one of my concerns about Harper was that he's never, EVER had to deal with struggles on a baseball field. He'll certainly struggle at some point in his major league career, so it's good to have him deal with some struggles down there so he learns some coping methods and can adapt those to his struggles when he's a major leaguer.
Dear Nats: Let him deal with his struggles down there, but after he comes out of it, he needs to be promoted. New challenges and all that!