Separate games mean nothing. Maybe PSG was exhausted by the previous games plus everyone predicted an easy win for PSG and this led to the burnout of the PSG players. But even if Chelsea is really stronger than the best team of the season at the moment, this does not automatically mean good prospects ahead. Bookmakers quote Chelsea's chances of winning the title as 1 to 13. I think you will agree that against the background of City, which went into crisis, the fresh champion and Arsenal, which have passed their peak, this looks like a very weak quote.
PSG getting exhausted by their previous games is not an excuse for the defeat they conceded against Chelsea because Chelsea were also exhausted by their previous games, but they were able to beat PSG in the Club World Cup final. Chelsea beating PSG doesn't justify that Chelsea will perform well next season, but you should allow them to enjoy their win against PSG while it lasts.
Chelsea over power Paris Saint Germain players that make them to lost against Chelsea in the final match. I know Paris Saint Germain players were very active in winning matches to arrived in the FIFA club world cup final because they never experienced any defeat from any team which is the reason Paris Saint Germain fans said that Paris Saint Germain players gotten exhausted
in before the final match, which is not the reason Chelsea defeated Paris Saint Germain, Chelsea coach plan ahead of the match because he was benching some of his players that use to cause yellow card and red cards in some match, and he maintain that good plan that make Paris Saint Germain not to take advantage of those cards to score a single goal, I have that confidence that Chelsea will play well in the premier League competition next season.