I think it is still quite early to conclude that a team's performance is in a worse direction because the team you mentioned could make a breakthrough again next season, although I am also not sure that Borussia Dortmund will reach the Champions League final again. However, we also have to understand that it is not impossible for Borussia Dortmund to repeat this as long as they have the ability and a much higher level of luck next season. Because last season, few people predicted that Borussia Dortmund would reach the Champions League final, but in reality they could get there.
Borussia Dortmund is not the top team in Europe even though they are top in the Bundesliga. I'm sure many people didn't expect them to make it to the UCL final this season. Some said they were lucky in some situations against Barcelona or PSG. But for me luck is also a skill of every team. I think it will be difficult for them to reach the UCL final again next season. This is different from Real Madrid which is the most successful team in the UCL. They are Europe's top team and their chances of reaching the final again are very high.
In last season, Borussia Dortmund were lucky enough to have spot into Champions League final despite having their poor show into Bundesliga with things were completely favourable for them in UEFA Champions League which allow them to have good performance against teams like PSG and Atlético Madrid, but now things are having good change and after having poor run in Bundesliga they are improving their squad for the next season which is good change because we are having tough challenges ahead for the all clubs.
Borussia Dortmund which is having business model on basis of having young players and sell them after development can't comparable with top sides in Europe which are doing amazing stuff for the years and having good success as well.