User blog:MrAnimefan/Why Luffy gets tied up?

There's something that bothers me about the 618 chapter. In the long history of One Piece, Luffy gets tied up many times, but after 2 years trainig and complete control over his Haki I though he can't get tied up SO easy anymore.

Tell me what you think about. Isn't Luffy strong enough or Oda tried to make a tough situation when the chapter didn't need one?