Last year the circumstances were also very special in the EL. This year they are in a neat 4th place in the league, and the differences with the teams above and below are minimal. They could therefore still be 2nd in this competition. It is the club with the most self-confidence after Bayern Munich. Because how much confidence should you have if you have wintered in the Cl and that you are also the current title holder of the EL?
For the second position in the Bundesliga it is still very possible for Frankfurt in terms of getting it. But for the Champions League, I see Frankfurt getting a very tough opponent this season, namely Napoli who have never lost this season in Serie A. So Frankfurt has a very tough task this season, especially in the Champions League because Frankfurt needs to really focused and consistent in order to beat Napoli in the Champions League this season.
I can't think that Frankfurt will be able to go far in the Champions League because as you said their opponents in the Champions League are a very extraordinary team. Even if they can beat Napoli in this round, their next opponent will be a team that is far stronger for sure. Although it is possible that they will give a surprise, but with the existing reality it will be very difficult for them to do so.