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.
Hansi Flick main focus is definitely to win the match and maintain the momentum of the team which is positive at the moment, while Revenge I think it is not the main goal of Hansi Flick remembering when Munich won big over Barcelona (8-2) he was the coach of Munich at that time, I think Hansi Flick will still aim for victory in the match while still avoiding his players from injury, Because currently Barcelona is required to be able to maintain the depth of its squad in order to remain consistent in every match they play in all competition.
Matches against strong teams like Bayern are often tighter considering the quality of the squad they have, so I think Hansi Flick should not try to aim for a big victory in the match, because it will only drain the energy of his players which will an impact on injuries.