You are right, BOrussia Dortmund is not the mediocre team mentioned, they are one of the top clubs which is experiencing a decline this season, so they have to be in a position they are not used to, because usually they are always in 2nd place in the standings. This is a match that will not be easy for Bayern Munich, because they have to face a club that is their rival. What makes them at an advantage is that the club they will face this time is not as strong as the previous season, but still they cannot just underestimate Borussia Dortmund.
Apart from this match, they also have a match that is no less important in the Champions League, because the result of that match will really determine their position, whether they will still be in the Champions League, or whether they will have to pack up and be eliminated from the Champions League. Looking at their opportunities in 2 different competitions, it looks like Bayern Munich will focus more on the Champions League, because in the Bundesliga their chances of becoming champions are almost closed.
Tuchel remains ambitious to beat Dortmund at the Allianz Arena, and continue to pressure Leverkusen at the top of the standings until the end of the season. Dortmund cannot be underestimated, they currently really need an additional 3 points to maintain their position in the top four of the standings. If you look at the statistics of both teams in their last five matches, both have recorded exactly the same number of wins, draws and losses. However, Bayern Munich will still be the favorite because they will act as hosts, the depth of Tuchel squad can make it easier for them to secure full points.
Apart from that, Bayern Munich will certainly maximize their potential in the Champions League, because their chances of winning the Bundesliga trophy are very low. To be honest, Dortmund are also faced with the same situation, in which I think both of them will be more focused on the Champions League at this time. Leipzig certainly hopes that Bayern Munich can beat Dortmund, because they will have the opportunity to penetrate the top four of the standings if the scenario goes according to predictions. Dortmund is having difficulty appearing consistently this season due to its own actions, which like to release important players in every transfer window.