I don’t think Ten Hag will be able to seriously challenge for the Bundesliga title next season. Alonso showed this year that when Bayern worked with Kompany, they became much stronger, meaning Bayern overcame their crisis and competing with a team like that has become extremely difficult. After Alonso’s departure, the situation could get even tougher. Plus we will need to see how well they manage to keep their key players and how Ten Hag handles the transfer market. He is a good coach and he built a strong reputation before his time in Manchester, but I am not sure that is enough for Leverkusen to win the title again.
Not only you and probably most people doubt Ten Hag because he had a failure at Manchester United but we need to trust him and hope he can do much better. Kompany also did not prove to be a great coach when he came to Bayern Munich but he was able to give his best slowly. What made Kompany who he is now is because he has the support and quality players in the team. This is what Leverkusen's management needs to do so that Ten Hag can also give his best for the club's success. If he was able to achieve success as Ajax coach why not give him the chance to achieve success at Leverkusen.