The Europa League final was a big learning for them. It was a huge disappointment for sure, but I believe that Leverkusen might have underestimated a challenge for the first time. In every game they were on point and you could see that they don't underestimate their opponents. But in this case I saw a game for the second time actually that they didn't do the job as well as they used to do it. First time was against Qarabag when they almost lost a game that they should never lose. They turned it around.
Against Atalanta though they had a team that knew how to defend a lead and how to play it till the end on the highest and most efficient level.
The loss of three goals in the final was a surprise for me. Leverkusen being favorite was because of their unbeaten performances, but both teams didn't have a big gap of quality. It's fair to say that Leverkusen might have underestimated Atalanta when Atalanta was actually a very good team with a very strong consistency in the last games at the time.
The late goals in several games that kept Leverkusen stayed unbeaten gave me impression that Leverkusen was not ready to play against a team that has ability to give a consistent fight throughout a ninety minutes display. This was what made Atalanta looked s strong in the final, when they were considered less favorite to win the trophy of Europa League.