In Ligue 1, what you said is true, other clubs are too weak and barely can have good seasons to challenge PSG and beat this giant club. PSG many times had their bad matches but they still completed those seasons with titles because other clubs are too weak to take advantage of PSG's poor performances. In domestic league, PSG easily won titles but it becomes their weaknesses when they play in Champions League. Being familiar with lower quality of matches in Ligue 1 and weak opponents there, they don't have enough quality, carefulness and preparations for tough matches in Champions League.
PSG fought really hard each season to become the UCL Champs but it seems their hardwork is not good enough and I guess it's time for them to upgrade their level of football. PSG are not serious in their league matches, they have top priority, and it's lifting the UEFA Champions League trophy, this is the exact scenario that PSG president, Nasser Al-Khelaifi have been working on, it doesn't last long to watch PSG getting eliminated, however this is new season and It comes with lots of surprises. Other clubs don't possess the big force to drive to becoming threats for Paris Saint-Germain.