Actually, there are also some other team that can always perform well but they only survive and compete for the second to the top 4 positions and that happens more often alternately, for the competition at the top of the standings it will be difficult for us to find impressively and this season Marseille is actually considered challenger to PSG that is worthy of consideration considering their impressive start to the season.
After some time, Marseille finally relaxed little and PSG rose again by taking the top of the standings, yes I completely agree with you that when the season changes Marseille can make another successful transfer then next season it is possible that they can be on par with PSG in terms of game quality.
For the runner-up position, it may be filled alternately by several teams for each season but if you look at who will come out as the winner of the trophy, PSG is the only team that has a chance. This is why Ligue 1 needs a change because if the challenger team is only able to play and end the season as runner-up then this league will never be as competitive as other leagues that alternately have champion candidates for each season.
This season Marseille has performed more impressively but has still not been able to surpass the capacity of PSG so we can conclude before the season ends that PSG's dominance is still quite difficult to break, let alone talking about the competition for the Ligue 1 title.