Union Berlin was my favorite team this season and I was even hoping to see them at the top of the table and racing with Bayern Munich until last week when saw them having a bad performance because of having not enough potential for the rest of the season.
I think Union Berlin could have much better transfers and they could hire better players to help them in this situation.
https://en.wikipedia.org/wiki/2021%E2%80%9322_1._FC_Union_Berlin_season#Transfers
There's no doubt that Union Berlin performed well this season especially during the start of the season and I can remember that they have been at the top of the table and have contested in several ways but it is unfortunate they were not the Champions and it is fortunate that they will appear in the Champions League. I think Union Berlin could have much better transfers and they could hire better players to help them in this situation.
https://en.wikipedia.org/wiki/2021%E2%80%9322_1._FC_Union_Berlin_season#Transfers
The reason why they fluctuated in their performance was lack of squad depth. I believe they will fix the problem this season by signing more good players and players will likely reciprocate because they are now in European competition.