Yes it can be said that big teams definitely make mistakes in final matches, as the final match between Chelsea and PSG already proves. In reality they have a lot of nervous stress and the opponent's tactical plan forces them to make mistakes, maybe that's what PSG did. It can be said that After winning this match, Chelsea will continue to be more intense next season as their team is already very well established. So maybe no one will underestimate this team in next season's Premier League because then they will definitely become more dangerous, even this team gave more responsibility to the young players with sharp knowledge in the final match of the Club World Cup, maybe we can hope that they will leave signs of their sharpness in the upcoming Premier League as well.
If you ask me I don't think PSG made any mistake in that game, they stick to their normal game plan and strategy that worked against every other team but just because it didn't work against Chelsea doesn't mean they made a mistake. Chelsea only approached the game with well planned strategy but PSG didn't do much they used their normal game plan forgetting that it's a final and everyone is supposed to come well prepared.
Because you are the favorite doesn't mean you should not study your opponent style and try to counter it. This was what Chelsea did and they came out on top. Kudos to Enzo Maresca for doing a fantastic job.
Of course Chelsea will be more challenging next season and I even expect them to challenge for the league because they have shown some growth recently and are capable of challenging for the title now, the team looks more experienced now.