They say that 2-0 is the most dangerous lead, but Barcelona are sitting pretty after a Lionel Messi brace against Arsenal. Despite their defensive struggles at different points, the Blaugrana have only conceded 2 or more goals six times this season.
In addition, Barça have only shipped 2 goals at home two times, and never more than that. Neither was a loss. One was a 5-2 beating handed to Rayo Vallecano, while the other was a 2-2 draw against Deportivo, conditioned by the fact that the team switched off late after getting a 2-0 lead, as it was preparing to embark on a trip to the Club World Cup.
Barcelona did concede 4 goals on three different occasions this season, which is quite worrying for Luis Enrique. But all of them were away from the Camp Nou, and the most recent one was in September. It could be argued that those were an early-season blip and it's all settled now.
Not only that, but the last time Barcelona conceded two goals was in December, in that 2-2 draw against Depor. Since that match, Barcelona have conceded only about 0.57 goals per game. For comparison, Atletico Madrid - maybe the finest defensive unit this season - has conceded 0.41 per game in La Liga. Paris Saint-Germain, who are super-dominant in Ligue 1, have conceded 0.5 goals per game in the French league. Bayern Munich's record in the Bundesliga is the same, 0.5 goals per game.
Barça's defensive record in this time span doesn't quite hit those lofty heights, but it's awfully close for a team that many assume is just about 8 random guys and Lionel Messi, Luis Suarez, and Neymar.
If Gerard Pique's absence isn't felt too strongly, it's unlikely even Arsenal will have the firepower to turn this around.