I've also asked myself the same question many times. What happens in Ligue 1 is unique. In the other leagues we see at least 2 teams or more competing for the title, but in Ligue 1 there is only 1 team and the other teams don't make big signings. Every time Ligue 1 starts, I don't have high expectations, so I already know that PSG will be champion and will have a guaranteed place in the European Champions League. The only thing I keep thinking: how many points ahead will PSG finish compared to the second place.
PSG domination in Ligue 1 is more severe than domination of Bayern Munich in Bundesliga. PSG lost less titles in domestic league than Bayern Munich lost in Bundesliga. In seasons they won domestic leagues, PSG have very strong domination in Ligue 1 and as you said, no actual competitor in Ligue 1 against PSG, while in Bundesliga, sometimes there are clubs that compete seriously with Bayern Munich even at the season ending they lose with big point difference under Bayern Munich.
This kind of strong domination in Ligue 1 is harmful for PSG when they play in UEFA Champions League because their star players are not familiar with tough matches and highest competitiveness. They are familiar with domination in Ligue 1 and lack of necessary concentration when playing in Champions League. Playing against giants in Champions League, lack of concentration within several minutes costs them a loss and it happens many times for PSG.
In the Bundesliga, Bayern Munich has never been able to single-handedly dominate, but if Bayern Munich has performed well in this league in one season, other teams including Dortmund have performed well, but in the case of PSG, it is completely different. PSG is the only team in the France league that easily wins the local league title and no other team can usually compete with PSG very much. For the past few seasons, I have seen that PSG does not have any additional plans for this local league. They started the season with whichever team they started and performed with that team gradually moved forward and at the end of the season PSG were winning the France league title by a huge margin.