Bayer Leverkusen is one of the clubs that opponents fear in the Bundesliga. Not all clubs can beat Laverkusen easily because they were at the top of the standings last year with good performance. It would be really good, as you said, that Laverkusen should add several senior players and star players, especially strikers and defensive midfielders, so that they can be more confident of winning this season.
Even though Bayern Leverkusen lost some of their matches, they are unable to keep the same energy as last season. I don’t think it is necessary for Bayern Leverkusen to add another senior player to them. They are still strong and one of the biggest and most competitive teams in the Bundesliga this season. Bayern Leverkusen will obviously face a tough season this season,
even if they will be the winner of the title at the end, but the season just got started; we can’t conclude on that, but to me, Bayer Leverkusen's still strong squad is not compulsory; they should add other senior players, as you said.
Although I know that it will help them in one way or another, I believe they can still go to the top with the same squad they are currently playing; they don't have a have a weak position; they are still competitive like last season, so as it is now, Bayer Leverkusen did not necessarily need any other players to join them before they made things possible for themselves. The coach knows that the current squad can still do it.