Teams like PSG can borrow a leave from Inter Milan if they want to some day become very formidable in the champions league such that they can dare you win the UCL, with a good level of consistency and continued improvement, inter Milan will be able to get to the point where even if they are not contending the UCL so well this season, they will be able to do much better by next season and of course they are sure to win or finish top four in the serie A this season.
PSG will run into the same problems over and over again. Inter Milan has competition in Serie A, PSG doesn't have any competition in Ligue 1.
For Inter Milan there is Juventus Turin, AC Milan, teams like Napoli and Roma, and in general the average quality of the teams is higher, which means that Inter Milan gets constantly pushed throughout the season.
Even if PSG were to copy a few things from Inter Milan, it doesn't change the fact that there is no team pushing PSG to play their best every single weekend and be ready for the showdowns in the Champions League.