you are right Despite PSG's squad having plenty of star players, their performances were poor. This is because there was not a good relationship between the players. Mbappe's relationship with Messi and Neymar was not good. Also Mbappe played selfishly. Because of these reasons, the coach failed to bring stability to PSG's performance. But now Luis Enrique is not interested in spending too much money. He first wants to create a good match strategy, and strengthen the bond between the players. Luis Enrique will then look to improve his squad's capabilities as the players bond. Will strengthen the squad by adding star players to the squad.
I would not say that Mbappe - Messi - Neymar performance was poor as they had combined 90 scorer points in Ligue 1. I guess it will be hard to find another attacking trio with 90 scorer points in a season in the league only. That's without Coup de France and without the Champions League. But they have still lost too many games and I think conceded too many goals as a top team.
In the game against Bayern Munich in the Champions League round of 16 PSG almost didn't have a chance despite all the star players. The difference in their performances was unexpected and must have also been disappointing for everyone who was looking forward to PSG delivering some nice games. I guess this season won't be any different.