What is clear is that there must be changes happening at Bayern Munich because they have a new coach but we don't know whether it will be better or worse. What is clear is that Leverkusen may still be a title challenger for Bayern Munich because the club is still coached by Xabi Alonso who has great tactical prowess coaching a club like Leverkusen. I believe Xabi will do the same as what happened to Leverkusen last season because he still has great players in him and has a winning mentality because he tasted the title last season.
But Xabi Alonso will have a tougher challenge, he has to divide his focus to play in the big Champions League competition. Hopefully it doesn't affect Leverkusen's performance because last season Leverkusen also divided its focus in the Europa League but still performed well, but the challenge next season will be tougher because The Champions League is tougher than the European League. But if Leverkusen unable in the Champions League, they should focus on the Bundesliga to get another title rather than having to push in two competitions. I'm not sure that Leverkusen's performance will be good in the Champions League because it will be against more experienced clubs.
Of course, all teams that have new coaches hope to be better than before, including the fans of each team who of course also hope that their proud team will show the best. with Bayern Munich failing to win a trophy, of course it disappointed their fans, but I think the brand's fans can still accept it because just this season they failed to win a trophy, of course they definitely want Bayern Munich back to its glory days, but it's true that you say Leverkusen is still a title challenger for Bayern Munich.
It's true what you said, Xabi Alonso certainly has to be able to balance his focus. With this, Xabi Alonso can definitely do it well, they still have to be able to appear consistent in both. I don't think Leverkusen will experience a decline, but in the Champions League they might have difficulty competing because the teams they will face are big teams. This is actually a good opportunity for Leverkusen, because they will face an experienced team that can sharpen their mentality to become better.