I agree with your opinion. The players in the attack and midfield really showed their best abilities, this was reflected in the four goals scored against Villarreal. Indeed, Torres and his friends really stole the attention with their extraordinary performances as young Barcelona attackers. Pedri's absence due to injury naturally leaves a gap in the squad. However, you are right in saying that if he had played, Barcelona could have done even better. The team's success in this match also shows a very good potential for victory. It's true that Xavi has to improve Barcelona's back line and defense so he can hold and read the opponent's movements, because Barcelona's back line is very fragile. The strategic approach to the game seems to be working, and if the consistency of the player's performance can be maintained, then Barcelona's chances of doing well in a competition like the Champions League are certainly very likely to occur.
Something they still need to improve on, yes it's their defense. I wouldn't say they were lucky in this game, because their offense is good, but they can't keep conceding so much. I see it like this, if they get an opponent whose defense is stronger, while their defense is fragile so easily broken it will be a defeat for them.
There must be a balance between defense and attack, not to mention their midfield. And now they have a good attack and midfield, it's just that their defense hasn't really played well.