I can't say if Chelsea has improved in their performance or not, it's when the new season starts is when we would know. However, their performance in CWC is impressive and their fate will be tested in the finals when they play against PSG who have destroyed and humiliated top big clubs in various leagues in recent times.
The season haven’t started yet, so we can’t conclude yet that Chelsea performance has improved, but even as they have been playing against weaker teams in the FIFA club world club, I can see that Chelsea performance has improved a little bit. The Chelsea which I know few seasons ago, even when playing against weaker teams, their performance is always poor, but with Chelsea players are now having confidence when playing, not like before that we are going to see them making mistakes.
Even if the season starts, it's a bit too early to comment on Chelsea's performance. At least until the league has settled down, it's unclear how Chelsea will fare. They're generally better than before, more confident, and won't suffer consecutive defeats against bad teams this season. Chelsea needs to show some resilience in midfield.
If they're as ineffective as Real Madrid, which they will be, PSG will easily take the lead. This lead could even be achieved in the early stages.