Chelsea vs PSG final is like the popular opinion but like you rightly said, it is not a good idea to assume that Real Madrid is a push over for PSG because Real Madrid is a good team and have demonstrated that in the few recent matches. If at the end of the day Madrid wins PSG, it will not come to me as so much shock because Madrid is capable of achieving that against PSG the European champion. Both teams have quality players, almost same grade of players so it will be a very big match to watch that day.
What is the guarantee that Chelsea will even beat Fluminense FC? The Brazilian side has proved to be a strong side that shouldn't be underrated. They were able to beat Inter Milan by two goals, so Chelsea should be ready for a fight.
I will not conclude that PSG will defeat Real Madrid. Maybe because of their recent exploit in the UEFA Champions League. Los Blancos have what it takes to surprise the current European champions.
There is no guarantee about Chelsea reaching the finals, everything is just speculation based on available information. Chelsea indeed seems to be the favorite to win Fluminense, although it is not guaranteed as it is obvious that Fluminense have the quality of players to defeat Chelsea as well. The same can be said about PSG vs Real Madrid because any of them can indeed win the match. What we are simply looking at is the probabilities for the various teams winning their matches and base on the performance of the teams, Chelsea and PSG seems to be the favorite for the final.