They are still a young team, which explains their current situation. Barcelona haven't stabilised yet and progressing with such a situation is difficult. Barca fans may feel uncertain about this team, especially if they look at Barca back-line.
Their problem is that they haven't found Pique's replacement. Pique is already 35 years old and his physique has declined. Even Pique always has a hard time facing a striker who can run quickly. I think Xavi should start thinking about the central defender. I think he should be brave to start the rotation,for example by installing Kounde as the starting line up. Because Xavi is carrying a mission of improvement and he deserves to give more playing time to the younger defenders.
They can actually find young defenders. I'm sure Xavi is following the Bundesliga and Serie A. From here, he can assemble a young defender with the features he wants into the team. Pique's performance may be one or two more years, nothing more. A young and strong defender with advanced physical features makes Barcelona very comfortable in high-level matches.