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.
That's what makes Xabi become one of the best young coaches in the world today. Because PSV has a style of play that suits what Xabi wants in his football philosophy. Even though he doesn't have any famous star players, or maybe I don't know him, Xabi was able to build strong chemistry between the players and in the end they were able to adopt the tactics and style of play that Xabi wanted.