Bayer Leverkusen letting Xabi Alonso join Real Madrid this season and also selling some of their best players to other clubs this season, I agree that Bayer Leverkusen won't be a problem for Bayern Munich next season, and Bayern Munich will continue their dominance in the Bundesliga league because Erik Ten Hag needs to build up Bayer Leverkusen's squad to the level where they can be consistent in winning their matches and challenge Bayern Munich for the Bundesliga title.
Honestly xabi Alonso has earned it, moving to Madrid was a very good move and you cannot blame Leverkusen for allowing him, remember last season he almost made the move but somehow he decided to stay back and help the team grow which he did, they were not able to maintain the Bundesliga title but they finished up so well that they are now a champions league participants in the new season so literally they are in a good position regardless, selling off some of their key players too is also looking like a deliberate act to help them get the team positioned firmly financially, it could also be that their new coach will need née signings he can work with.