I will disagree with that statement that They d not have stars, I think they do have stars but it is not a star studded team like the Bayern Munich team. The likes of Xhaka are stars, Florian Writz is also a star already since his breakthrough last season and that’s why his Markets value is growing higher everyday. Also in the Bundesliga, Jonas Hoffman is a star too. This guy joined with the others have been the back bone of the team. Also at the defense i nearly forgot about Jonathan TAH who is also a rock solid defender for both club and country.
There is no star in Leverkusen. They're mostly just potential players.
Even Florian Writz who is their best player to me is not a star. He may be a star in the team, but he's not a star in world football.
A star player to me is a world class player that has proved himself in over 3 years. Writz can go to another team and not be a star despite how he has been good at Leverkusen.
Xhaka was at Arsenal for a long time but he was never world class, he not still among the top 10 players in his position in the world so how is he a star? There would be teams where he won't be among the first 11.
So it's safe to say there are no proven star players in Leverkusen, even their coach is not a star coach.