I wouldn't write off Barca just yet. Atletico are a great defensive team, and they nearly outdid themselves yesterday on that front. Which of the other remaining clubs in the CL could have mustered this kind of defense against Barca? Chelsea, maybe, but that's it, and probably not as consistent as Atletico either. Sure, Barca do have their weaknesses (not the least of them defensively), but one could hardly expect them to score four or five goals against Atletico.
It's a dangerous result for Barcelona going into the second leg, that of course is true.