Next season will be far more difficult because defending the title is not easy because there are many challenges that will be faced by PSG. For competition in Ligue 1 I am not so worried because there are almost no other teams that are able to break the dominance of PSG and overall the players they have are much better.
Winning a title after a long time can even look easier than defending it because at that time you are only contending for the trophy as against a few pressure around but when it happens that you are to defend the title, I bet you will be under some for more pressure than you were in when attempting to win only because both your opponents, the fans and everyone gat theieyes on you to see what you are doing to win back the trophy so they will all keep tabs on you morethan they would much before.
The Ligue 1 will be more competitive next season and I think PSG might struggle in defending their title because clubs like Monaco which Paul pogba will play for next season are strengthening their squad in the transfer window which might be a potential challenge for PSG in the league.
Marseille will also perform great in the league next season and so PSG now have more stronger squad that will compete against them for the trophy but nevertheless PSG is a strong team that has a good squad and even with the rising competition in the league they might still defend their title next season.