The depth of the squad can be something important for Ten Hag because next season they will play as one of the title contenders and if the current transfer market is not utilized well, it will be difficult to compete with Bayern Munich who are currently growing. For the Champions League, I do not favor Leverkusen next season because there are many things that make them look not so favorites. Ten Hag certainly deserves a chance but don't expect too much in terms of titles because the new manager will definitely need to adjust to the pace of competition in the League.
You need to first have a starting eleven before you can even think of squad depth, but as it is now some important players is already leaving the team and when new ones come they at least will need little time to adapt to the new coach tactics. I don't think Bayern Leverkusen will be able to compete with the likes of Bayern Munich as they did this season and the last because of the change of manager. The stake at the club will be high now because of what Alonso has done.