That's true, and I'm not surprised a team like PSG couldn't win the Champions League when they still had so many star players, including Messi, Neymar, and Mbappé. But when they were no longer in the team, PSG won the Champions League straight away last season, and that's a pretty good example to illustrate your point. So, star players, whether they're not star players or not, must be able to work together to bring victory to the team, because the team doesn't teach them to play individually, ignoring their teammates.
Whenever a team has got too many star players, there is always a conflict of position and interference of personal interest from these players so it will be very common to see the team struggling at some point but most crucial goal which was supposed to getting the team to doing better will mostly be defeated in most cases but if they are able to play together in a good team spirit of which the coach has got a huge role to play in this, then the cluster of stars will be an advantage for the team.