It is true that the chemistry that Xabi Alonso has built with all the players in the Leverkusen squad is strong enough so that they can carry out their strategy quite well and in my opinion that is the key to their success to date, even though if you look at the depth of their squad there are no star players, however Their team's performance this season has been extraordinary.
And Xabi Alonso built this team not only this season but since his arrival in the middle of last season, so it's only natural that this season they are quite solid.
Regardless of what happens now for Leverkusen there are indeed several thing that support them to get to this position apart from the experience they have before, the good chemistry between Xabi and the players make Leverkusen what it is now.
But talking about star players at Leverkusen i actually don't really agree with what you said because after all by looking at the players they have there are actually several players whose quality is above average, such as Wirtz, who in fact is one of the young players who has great potential in Leverkusen and in his own country Germany. In addition there is the name Palacios which we know he is one of the Argentine midfielders who won the world cup which certainly has quite good skills and there is the name Xhaka who is actually a figure who has more experience for Leverkusen. Even though they can still be said to be smaller than some big names like Kane or even Cristiano and Messi they are one of the Leverkusen players who can be said to be stars to date because the quality of their skills is still above average.