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.
You are right that Chelsea young squad and their inconsistency are big issues for their Champions League hopes. But their past win showed they can surprise everyone even when struggling in league winning single Club World Cup match does not mean they will succeed in Champions League. That tournament demands top performance week after week something their young players still need to prove they can deliver.
It is true that Chelsea Football Club is a young team but there is no inconsistency between them, they have also been showing steadfast in their club friendly matches in preparation for the upcoming season, from their Club World Cup matches. Their past victories show that they can surprise everyone and if they struggle, the Champions League will definitely consider them as tough opponents. This tournament definitely demands the best performance so it is almost certain that their young players will be able to prove themselves there, because we have seen them win comfortably against high-profile teams in two club friendly matches recently, they had mainly satisfying wins when facing Italian clubs and Bayer Leverkusen.
Not a Chelsea fan but sometimes I love the way they play and the enthusiasm. judging with the current performance of all the English team in the premier league I see Chelsea as the best as it stance, there are matches I was thinking they can not be able win in this club friendly but they have proved me wrong and have been defeating teams, imagine the result they got with AC Milan that was an amazing result and I was not expecting that kind of result. The truth is Chelsea is back based on what I have seen and the premier league will be very strong and the champions league won't be easy with any club that will play against Chelsea.