It's not just about the experience of a particular tournament, but also about the level of the opponents, as well as the form in which the team is. The Champions League will certainly be the most difficult test for the team and for Alonso, because one season can be completed on luck and courage, and you can earn recognition if the team can repeat the success again. And if we are talking about success, then the Bayer could not achieve it in the EL final, and Atalanta is not the strongest team, in the Champions League the opponents will be much more difficult.
This will be a real challenge for Xabi Alonso, he has to prove to everyone that what he achieved this season was not luck but was the result of the hard work of himself and the players. Because currently there are still many narratives that say that, but it is normal because those who say that are people who want to see whether Leverkusen can do the same thing or not.
In my opinion, it is very difficult to be able to repeat the same thing by only achieving 1 defeat from all the matches they played, but at least they can be consistent by achieving many positive results or not the opposite results this season. Because there are many teams that can only show impressive performance in just one season, while in the following season they fail to give their best and they even decline very sharply. We can see Napoli in Serie A, Sevilla in La Liga and many more teams showing performance like that.