Judging by the quality of their current squad, I agree that Chelsea isn't a contender for the Champions League title this season because some of their players are still quite young and inexperienced. However, if you look at the club's history, they have won the Champions League before, despite their performance declining significantly in the Premier League. Beating PSG in the Club World Cup doesn't guarantee Chelsea has a much better chance in the Champions League, as they sometimes play well and then miss opportunities to maintain consistency.
A team like Chelsea should not be underestimated, as they can still cause unexpected upsets in major competitions like the Champions League. And PSG experienced this in the Club World Cup, where they were completely humiliated by the team that won last season's Conference League. So, underestimating a team like Chelsea can sometimes be a fatal mistake, as Chelsea have been able to embarrass teams that won last season's Champions League in a competition that is no small feat.
Chelsea have seen steady improvement since Maresca's arrival, and their success in winning the Club World Cup should be a good indicator that they can do the same in next season's Champions League.
You're right, as you said, Chelsea shouldn't be underestimated. Personally, I'm quite confident in Chelsea, and they deserve to be placed among the favorites to win next season's Champions League. If that happens, it wouldn't be a surprise, as Chelsea have a pretty strong squad right now.