Xabi has been with Leverkusen for almost 3 years, so he can get to this point in need of a process. So if Bayern want instant results it seems that is also difficult to happen. Because I believe Every coach must have a process, there are not many coaches who can give a champion when he just comes. So if Bayern want him, it is also the same as the previous coach because there is no definite guarantee from Xabi.
Xabi Alonso joined Leverkusen in October 2022. It is the second season of Xabi Alonso managing Leverkusen squad. It is true that Xabi Alonso doesn't suddenly succeed with Leverkusen. He needs 1 season before he can succeed to lead Leverkusen be the champion. In his first season, he only can make Leverkusen to finish in 6th place (Europa League zone). This season, Xabi Alonso could make a big difference for Leverkusen, he knows very well Leverkusen after spending 1 year with Leverkusen. Now, with the big point gap, no doubt that Leverkusen will be the champion in this season.
I think if he manages Bayern Munich, it won't be as difficult as Leverkusen. Bayern Munich has a great squad with many quality players. I believe Xabi Alonso can succeed there since his first season. Although there is no guarantee but I am very sure Xabi knows well Bundesliga competition and the quality of Bayern Munich squad.