Most of the clubs that have hard few crisis in the past, the outcome is always highly significant on the team overall performance, this is because most time, those clubs that faces much internal crisis always tend to be bad in performance take Manchester United for example, the Major reasons for Manchester United downfall in the few seasons past is because of internal crisis with in the club involving the coach at that time and a big player and ever since then, Manchester United have being struggling to get it footing on the ground again.
PSG and Manchester United are different clubs and they had different problems. Neymar, Cavani, Mbappe and Messi had more contributions for PSG than what Pogba did for Manchester United. They are more professional than Pogba and Manchester United made very decision by sacking Jose Mourinho and believed in Pogba. A few seasons later, they finally had to sell Pogba at cheap price as an unofficial admit of their severe failure with this star player.
So far, PSG generally are far more successful than Manchester United and they will maintain it in future while Manchester United are still building up with vague signs of future success.
Manchester United has unexplained problems. Absolutely every player that goes there, their quality drops to zero. Not only players but coaches too. This is really crazy cause once players leaves Manchester United, they immediately shine (when they arrive at their prime, they immediately decline). Antony is a good example, this man was playing well before moving to Man Utd and now he plays well after leaving Man Utd, just look at this video, what a banger goal:
https://streamin.me/v/296a20bePSG is doing very well, this club should not be compared to Man Utd but if we talk about club management, to my mind, Real Madrid is one of the best if not the best.