I think it was not because of a mistake that Atalanta beat Bayern Leverkusen in the Europa League finals. Before the Europa League finals, Atlanta was in amazing form, which helped Atalanta be in a better position to beat Bayern Leverkusen in the Europa League finals. And if it was a mistake that made Atalanta beat Bayern Leverkusen, the score of the Europa League finals would have been 1-0 or 2-1. The UEFA Champions League competition is a different competition from the Bundesliga. Bayern Leverkusen needs to be at their best performance if they want to qualify for the round of 16 because they will be playing against the best clubs from other European Leagues.
After Atlanta win Liverpool, they began to experience a boost in their performance and I believe their confidence grew even stronger which gat them believing they have got a chance to possibly win the Europa until they were able to make it to the finals and then they got to win the Europa. Leverkusen didn't make any mistake that Atlanta took advantage of in the final game, it will even be okay to say Leverkusen didn't have the best performance in that game, rather Atlanta did and was deserving of the victory which ear earned them the trophy.
I want to believe that, Leverkusen are going to do better this season even if the challenge has grown bigger as they are contending in a much bigger league than the Europa which they earlier did compete in last season, if Leverkusen gets stronger this season, I believe there's more they can achieve than they did last season, they now have a strategy with they can use to maintain firmness to the point of avoiding frequent losses enough to get them in the position they most desire to be and win more games as they should and possibly dare to aim at the trophy.