It's a big mistake from the management of Bayer Leverkusen to let Xabi Alonso leave the team after losing their key players that helped them to win the league, they may not have had what it takes to keep Xabi Alonso for many more seasons but allowing him to leave when they have lost so many players will definitely affect the team because the new manager will start a fresh to build the team and they may not be able to contest for the league title next season.
What is a good manager without good players. It is also a good way of allowing the new manager Erik ten Hag choose his squad according to his formations. Xabi Alonso wasn't demanding anything the club needed for him to stay, it was a fair departure from the club and i don't see it different from this, now it is left for Erik ten Hag to retain their position as competitors for the Bundesliga title. My problem is that people will judge Erik ten Hag too early because of how bad his season went at Manchester United, quality time should be given to him since it is about rebuilding the team.