I think beating PSG 2-0 is a big achievement for a team like Rennes. PSG has two of the best players in the world Messi and Mbappe in the attack. Rennes' defenders were able to successfully block these two players. Rennes' defense was very solid in this match. And their match strategy was also excellent. However, this match made it clear that PSG has a lot of weaknesses within their squad. And coach Galtier completely failed to stabilize the team.
It is true that we are talking about a big achievement, but at the same time PSG didn't look like they were really into the game. They know they will win the title, they are aware that they lost in the UCL as well, which basically is a season over for them once again.
What are they going to play for after this moment? What would be the reason to go out and play as well as you can and give your 100% to every game? There is no need for that at all, there is absolutely no way that they are losing the league, the difference is 7 points and they won't give that, and UCL is done for them, so we will see them end up with a title situation where they won't have to play well enough to care.