Bayern Munich will remain a strong challenger to Leverkusen next season even though they do not have an experienced coach because in terms of experience Bayern Munich is a strong team with complete players in all positions. Leverkusen has the opportunity to retain the Bundesliga title as long as Xabi Alonso can maintain the quality of his players and not let the opportunity to play in the Champions League be an excuse for not playing consistently in the Bundesliga.
It's not easy to defend the title with the minimum number of players and last season's moments are difficult to repeat. Bayern Munich and Dortmund have new coaches so they have to be able to adapt beforehand so this is the best step for Leverkusen to maintain their title and play more solidly.
Bayer is doing without big transfers for now, they are not selling players, but they are not in a hurry to buy new, so far there are only rumors about possible purchases. I agree that Kompany is not a very experienced coach, but when Alonso came to Bayer, he was also not very experienced, but to gain experience you need to do something. The Kompany was entrusted with the position of a coach, perhaps there are risks in this, perhaps Bayern should invite a more experienced coach, but this is their choice.