I don't see any chance for this team to improve unless PSG changes their coach and finds an experienced coach. PSG management has a lot of money. They are also willing to spend a lot of money on buying players. But if there is no experienced coach, the performance of the team will not be good. And we've had proof of that in the last few seasons. PSG must now convince Zidane by any means necessary. If Zidane becomes the coach of PSG then I believe the overall situation of PSG will change. You don't need a lot of star players to win the Champions League title. What is needed is a stable squad and a good match strategy.
I think you are thinking it in a wrong way. A good coach is important and is like half of a club power but he can not do everything. The rest half belongs to players who actually play on field, play against opponents and they are who convert tactics and preparation of their coach to real show in a match.
About their players, to make a strong squad, they must have good balance between attacking and defense. You can easily see that they have never had that balance in their squad even they spent a lot of money for player transfers, player salary after many years. Their defense is weak compare the total budget they spent and to other big clubs. With that weak defense, including contributions for defense from their attacking players and midfielders, they are always fragile in Champions League as other big clubs can easily to exploit their defense weakness and beat PSG.
Zidane won't be able to fix it by himself and PSG must change their strategy to build their squad first.
You are right. It is not the case that a team will perform well only with the help of a coach. The squad players must play well. A good performance is not possible if the players do not play well.
However, PSG's poor performance this season is due to their poor match strategy. I noticed closely that PSG's match strategy was not good. The performance of the players in most of the matches seemed to me to be completely aimless. At the same time, their coach has changed PSG's formation many times. Its adverse effects have been seen in the team's performance. All this happened because of the inexperience of the PSG coach. I think if PSG had an experienced coach, their performance would have improved. Because they have this ability.