That's not what everyone thinks, at least those who understand that the Club World Cup is more or less meaningless as a predictor for next season. The teams still change, PSG lost 0-3 in the final and nobody would think that if PSG and Chelsea play against each other in the Champions League, the game would end like that. It was a brand new competition run in a rather unknown place with unknown surroundings. That's about as bad as it can get to be taken as a predictor for future events.
Yes we all can not agree less that Chelsea triumph against PSG which is currently the best and most organized team in the world, they Chelsea have raised in ranks then. Many of their fans will have their hopes high and are even backing the blues to actually go all the way in the Champions league. Personally I am not going to doubt their capability because even if they got the easier route to the club World Cup finals their performance against PSG in the final was a thing to boost of and also raise them to think that they can go all the way in this champions league because they think they have beaten the best.
Yes they have beaten the Best but this is champions league we all know how teams who are not even playing well in their respect leagues turning to a tough club to actually defeat. Take for example this same PSG team they were on the brink of been kicked out at the group stage but they sat up to win their first Champions league trophy which is a huge achievement for just any club