Exactly, if Alonso wants him to be continuously praised as a good coach, he needs to repeat the same thing he did in his first season at Bayern Leverkusen coaching them. At worst he should not be on the wrong side of the final result after the season. He is a respected coach more since he won the trophy without losing any match. He needs to continue that performance with them until he fully believe and make that impression to everyone that he can be the best coach everyone wants him to be and like other successful coaches and not just a lucky one as others might foresee it.
Alonso achievements this season have certainly made his career and also his prestige as a coach increase rapidly, coming as a young coach and underestimated after not having much experience in coaching, precisely now Alonso has shown everyone that he is indeed worthy of being counted as a great coach, Leverkusen this season has ended the season undefeated so this of course makes many parties amazed because with a makeshift squad Leverkusen was able to make new history in bundesliga football this season, Alonso ability to set strategies and also game tactics was of course able to optimize the performance of each of their players who were not star players.
The depth of the squad that Leverkusen has this season is of course very good even without star players, next season will be a difficult phase for Alonso to maintain Leverkusen performance, as you said, of course Leverkusen needs some additional players to be able to further improve the quality of their team, especially indeed Bayern Munich and other teams certainly have great ambitions to win the championship so they are currently also starting to improve their quality, Leverkusen seems like next season will no longer be as great as this season, because currently some of their main players are also interested in joining other teams.