I won't say that Barcelona's defense played badly in La Liga. But Barcelona should strengthen their defense a little more. Madrid is increasing their strength. If Barcelona wants to survive in the competition, they must strengthen their defense.
Hansi Flick knows the weaknesses of his squad very well. That is why he added Joan Garcia to the squad, Flick is no longer relying on Ter Stegen. In addition, Barcelona is going to buy Nico Williams as a replacement for Lewandowski. And now Barcelona will have to try to strengthen their defense. However, we have not seen Barcelona take any visible steps to strengthen their defense. However, Barcelona should definitely bring an experienced defender to the squad.
The defense is not bad but not perfect that's all, you know when most of the defense positions are entrusted to young players then basic mistakes will still happen, they are still learning to read the game, maintain consistency and communicate well, it takes time and experience for them to be really solid. The question is will Barcelona bring in an experienced defender to balance that line or stick to their stance of recruiting Nico? considering their problem is finances so I think what is most important for Barcelona now should be prioritized.