The Club World Cup is not a benchmark for teams competing in the Champions League because we can see a number of strong teams losing in this competition. PSG have indeed performed much better after winning the Champions League, but there's no guarantee that they will be able to defend their Champions League title back-to-back. There are still many things to consider to determine who will be a strong contender for next season's Champions League, as all teams are undergoing team overhauls.
But it's possible that PSG are much better than before, so they can perform much more convincingly in the competition, especially considering their performance when they beat Real Madrid in the Club World Cup.
But such a defeat certainly does not justify Real, they prepared well for the Club World Cup, tried to close the problematic positions, but yesterday's match showed that everything remained the same and they still concede a lot. Maybe if Militao and Carvajal could have played from the very beginning of the match, everything would have been different, but there is no certainty about this either, because they have been injured for too long and it will take him some time to fully return to the game. It is obvious that PSG is definitely stronger than them now, and if they also beat Chelsea, it will not surprise anyone.