That was precisely last season, Olympique Marseille seemed like the team that could challenge PSG for the ligue 1 title, they had some wonderful players in their squad and they did wonderfully well in the First half of that particular season which made them one of the favourites to lift the trophy but at the long run everything went bad when they started losing important games week after week, and numerous draws thereby giving PSG the opportunity to continue to dominate the league as usual, the rest is history.
My experience in Ligue 1 tells me that if PSG got 10 points gap by the 10th round then it is another classic season where PSG play alone and their rivals fail badly as usual.
PSG didn't change a lot, maybe the main change is the departure of Donnarumma to Manchester City and having another goalkeeper who is good too. I expect them to keep their titles, at least national ones.
Their opponents reinforced their squad but nothing very important since they can't spend without limit. The interesting transfer is for Giroud to Lille even though he is old now.