PSG has no rival in Ligue 1. They have nothing to worry about because every season is like a work over for them. Winning the trophy has become their tradition in the sense that they're used to winning it and will always add it in their yearly celebration activities, because no club can stop this from happening.
Other teams in the French Ligue 1 are also not ready to win the Ligue 1 trophy, and that is the reason why they always find it very hard to sign great players who can help build a better squad that can compete with PSG. This is one of the reasons why most people see Ligue 1 as a less competitive league because no other team can truly compete with PSG.What is even more telling is that in some seasons, PSG may not perform well at the beginning of the season, but by the end of the season, they still manage to win Ligue 1 and possibly other domestic cups. Even this season, I would say base on my observation from alk team in the ligue 1 competition that PSG has a 90% chances of winning the Ligue 1 trophy where Other teams, even those that seem serious, may have only around a 60% chances to win the league. This shows that their squads are still far behind PSG in terms of quality squad.
You're not far from the truth because if other teams in the French ligue 1 were actually serious about winning the league they would have taken seriouse steps in acquiring players that are top class who will be capable of challenging PSG when it comes to the league contention