Barca don't need to have the same performance of last season,if not they might not be able to win the next champions league. Barca needs to improve in their performance so that they can be hopeful to win UCL. The champions league is a competition that brings the best clubs from different leagues to play amongst themselves and more is expected from most clubs. Winning your local league hasn't given you a guarantee that with the same performance you will win a competition played by the best clubs in Europe. I still believed that with the little change in the players Barca will do perfectly well in the champions league this season. As they will want people to believe in them by impressing their fans with good results.
I don't see Barcelona winning the Champions League because the rating of their performance last season is very low. Even winning La Liga is luck to me because Real Madrid's attention was all on the Champions League and to some extent Madrid is also not serious, they played well during the first League against Manchester City and second leg i wonder what happened and they were clear beating by the city to qualify for the finals, I believe Barcelona should stick to La Liga since the Champions League is truly very competitive if you are not prepared, be prepared to dance to your own song outside of the league.
Barcelona's performance in the Champions League last season was disrupted because several players were injured. Their defense was a mess and it looked very different when they played for La Liga. Xavi tends to trust Alonso as a left-back compared to Balde or Jordi Alba, it's also a form of mistake because Alonso is not in good form as a newcomer.
I hope Xavi can really learn from Barcelona's mistakes and his strategy in the last two seasons in the Champions League, so he should have a good plan for next season's Champions League. But still, I don't think Barcelona has a big chance to win the Champions League title soon.
Some clubs need to start having serious back up against injuries, relying on a specific player on a specific position can be dangerous, Real Madrid suffered the same thing when Benzema went on injury, Alonso case the player needs to understand field communications to make team work more effective, Barcelona actually had some defaults last season, which is why I stated that winning even La Liga was pure luck. Personally, I don't see Barcelona winning the Champions League either; Inter Milan performed significantly better and may potentially have a chance this time.