Currently PSG face a life and death match against Barcelona in the second leg later, even if now PSG is really ready but I doubt if they can beat Barcelona in the second leg later, Mbappe continues to be PSG's mainstay so far so when Mbappe performs badly of course PSG will also end the match badly during this time, What you say is true, because whether or not a league is competitive at this time will make a team's mentality affected and just like PSG who play in a league is not competitive, of course it will make their mentality continue to be weak.
It seems that PSG chances of beating Barcelona in the second leg will be very low, unless Xavi squad plays badly throughout the match. Of course, this will not happen, because Barcelona will utilize all their potential to maintain their lead, and it is possible that they will win again. PSG failed to utilize the squad they had, what hurts was that they lost at home. It's no wonder we think their chances in the second leg are lower, even though PSG has Luis Enrique who understands Barcelona strengths very well.
PSG must play as a team, not always rely on Mbappe in every match. Players like Mbappe will of course be closely guarded by Barcelona players and this will limit their space for movement, here other players must be able to replace Mbappe role in making the difference. The competitive level of Ligue 1 is easy for PSG, but it is the main problem that makes them weak in European competition, with the depth of their star studded squad they should be able to show a different performance in the Champions League.