I tend to think that it is not Leverkusen who are in decline, maybe other rival clubs have improved, or maybe Xabi Alonso's style of play is no longer as effective as last season so it is difficult for him to maintain the team with the level of consistency of last season. Maybe bringing new faces into the squad can help Leverkusen navigate the Bundesliga better. Let's see in January if Leverkusen has such a plan.
Such a plan could be born on Leverkusen's side if the team has more funds to get involved in the transfer market in January and what you said is also quite reasonable that it is not Leverkusen who have declined, but rather it is more about the rivals in the Bundesliga who have been able to read Leverkusen's tactics themselves this season so that Leverkusen looks a little difficult to improve like they did last season. In addition, Bayern Munich who are coached by a new coach have also started to rise again so that has also become a very real obstacle for Leverkusen and also for the other teams in the Bundesliga this season.