I agree Barcelona might score more goals if they are ahead of Bayern to prove point. But coach Hansi Flick will focus on winning game not getting revenge. Flick wants to keep team momentum going while saving energy for other important matches in La Liga and Copa del Rey. Revenge sounds good but Barcelona main goal is to advance in Champions League. Winning convincingly will boost their confidence. If they focus too much on revenge they might get tired or hurt players which would be bad.
Barcelona scores a lot, but when the opponent is Bayern, it can be like in the match with Aston Villa, when everything is decided by one goal, or like with Bayer when there was a 1-1 draw, I mean that when the opponent is difficult, the game is different, there can be few goals. Bayern cannot win the last matches, maybe it is not a crisis, because they play very well, but something is clearly missing, and Barca, despite the losses, is still very good.