I agree that the decrease of Barcelona performance is caused by too many injured players. Some of them are the key players like Lewandowski, Kounde, Pedri, Frank de Jong, and Raphinha. However, some of them have recovered now, Lewandowski and Raphinha have played yesterday. But they need time to be back to their best shape. It is not easy to play again with their best after they spend much time for the recovery.
I think, losing Dembele and Ansu Fati also contributes to the decrease of Barcelona performance. I still remember that these players often give the difference when they played in big matches in the previous season. I am a bit confused why Xavi doesn't need them anymore. Xavi may not know that losing them will bring a big impact.
I agree with you, especially in the case of Dembele and Ansu Fati. Barcelona would have performed better with those guys if they were around. even though I won't easily discredit the efforts of the players that played yesterday match. But Barcelona should have envisaged the big match and could have add more efforts.
It was more of let's start hard and finish softly, yesterday. Like a case of we are in a hurry in the first half but have all the time to relax in the second half. If Barcelona had applied the same efforts they used in the first half, they would have performed more incredibly.