I think PSG's defense is not that good, but even so, it is very difficult for other teams to compete with PSG. PSG is far above the other teams in the league both in terms of quality and financial power.
PSG started the season badly but over time they started to play better. I criticized PSG a lot at the beginning of the league but now they are playing better football. So I won't criticize them too much.
Nice currently have 35 points and they are 5 points behind PSG. They cannot close this points difference easily. As the league progresses, PSG is less likely to lose points. The players and the team are adapting more and more to each other and they are winning series. I can say that Nice will have a difficult task to follow PSG.
They started poorly and I have no idea if they can be able to maintain the good standards set in the previous season. It's a difficult task for PSG to become winner's rather they had to settle for low budget if they would be keen to stand strong on their foundations keep lifting the Ligue One trophies. Paris Saint-Germain defendlines have problems and they're no longer classified as the formidable defend due to the presence of new players and new coach, they're yet to blend in good chemistry. Everyone have their pace and are trying their best to fit into the system of Les Parisiens.