In the past we have seen the Barcelona manager always try to build a very strong squad. And Barcelona dominated both La Liga and the Champions League. But after messi left the team, the scenario gradually changed. Barcelona coached Koeman. Koeman turned this team into rubble. The performance of the Barcelona team was very bad. Barcelona's performance gradually stabilized after Xavi took over. But still the Barcelona squad cannot be compared with the Munich or Manchester City squad. Also, while Xavi is undoubtedly a good coach now, he lacks the experience as a coach for a platform like the champions league. And so Barcelona cannot be considered as a favorite for the Champions League title this season as well. If the bonding between their players is stronger then maybe the team can do well in the Champions League as well.
Actually when saying Koeman is guilty it is also not entirely the fault of Koeman because he is still better than Quique Setién who could not even bring 1 trophy to Camp Nou and Koeman only continued but could not improve the same as Lampard did at Chelsea or Rangnick who became Manchester United coach.
The era of Barcelona's destruction began with Ernesto Valverde who left to be replaced by Setién who failed miserably at Barcelona coupled with poor management in terms of finance.
Now Xavi's job is to fix that, for the Champions League the last 2 seasons Xavi has completely failed and cannot contribute much because they always crumble in the group phase, this season must be a differentiator because if not then no matter how good Barcelona is in La Liga it will still be criticized when they fail again in the Champions League group phase.