Yes, Chelsea have really improved and this year they can return to the ranks of the big clubs in the Premier League and in Europe. They have amply demonstrated this and are still demonstrating it. I, on the other hand, think that Paris will suffer a regression, citing the team they beat.
PSG, who were defeated by Chelsea in the Club World Cup, will not immediately experience a setback when competing in the Champions League next season. PSG will also strive to win the Champions League trophy again, although it will be very difficult for PSG, as several other teams will also be doing the same next season. But generally speaking, PSG will not be immediately weakened just because of their defeat to Chelsea, although I also admit that Chelsea have indeed made quite positive changes recently.