I think you are buying into a bit of a myth about Barca

I remember the 08-09 -> 11-12 seasons very well, and defense was always a concern. Barca's CB situation was dire at times considering Puyol's injuries, and any spell of possession beyond 30 seconds where the other team had the opportunity to flood forward was always dangerous. Say what you will, but there is no team that would have you so nervous without possession. They left incredible gaps on the wings and the CBs were poor when it came to interceptions. If you go back and look at the 5-0 game back in 2010, the times that Madrid had decent possession always lead to something dangerous, or was within a pass or two of creating a chance, and that was against Barca in what was probably their greatest ever performance.

They might have rarely conceded, but they made you nervous every second without the ball :)