PSG is a very strong club financially but no matter how financially strong PSG is, they never want to lose money on player transfers. If a player moves to another club, the fee PSG receives for the player's transfer is a profit and PSG will never give it up. PSG spend huge amount of money to buy world class stars but due to their main focus on only world class stars they forget that world class attacking line up needs world class defense and midfield line up. If they hadn't forgotten this, they would never have bought world-class stars, they would have bought world-class stars and quality midfielders and defenders to make them a complete team. PSG is a team that has always failed in this perfection.
I don’t agree with you regarding the middle line, PSG has always had a very strong line, and the defense played poorly in some moments, because the team always placed the main emphasis on attack, and it is clear that in such cases their opponents tried to play on counter attacks, for defense it's always difficult. PSG have always spent a lot of money on players for all positions, their main problem still remains that the club owners have no patience, they simply do not give time to a new coach to form a strong team and change them every season.
When you have a team like PSG, it's hard to have a defense. Why? Because other teams usually close down, which means that they will be defending with at least 7-8 players, maybe who knows it could be more, I have seen all 11 players at their own half as well.
This means that you can't just attack with 3-4 players, that's not going to be enough and that's going to cause you some troubles, so you are going to end up putting all of your 10 players in there passing trying to find an open pass to shoot. This means that your defenders needs to come all the way up to the half way line, and that means when there is a counter attack you need to be incredibly fast to defend that player and try to stop them, it's a tough job.
The main problem for PSG to not getting good results in the past was mostly because of the unbalanced team they had, PSG had the best forwards however there was a negative atmosphere in the teams but they had the best forwards and they didn't get good results because in the other positions, and especially in the defensive line they didn't have good player, I think this teams still don't have good defender and you can see this problem when they are going to play in the Champions League against strongest teams.