Dembele is also a great player, although Mbappe is much better known as a world striker. PSG also once had a number of world star players at the club, but they also failed to become champion candidates. Luis Enrique needs to build a better squad and must prioritize collectivity over individual skill and he needs to learn a lot from what Pep Guardiola did at Manchester City because their squad is also not strengthened by world star players.
City is a great club. But this season they seem to be having difficulties when their main players are injured. This can be seen from their last 5 matches when Haaland and Kevin De Bruyne suffered injuries. I'm afraid they won't be able to go further in the champions league this season. And for PSG I agree with what you said that they only have Mbappe as a world class striker although I also don't underestimate Dembele. But the problem at PSG is how Enrique makes collective team play because I see that currently they still only rely on one or two players in their game tactics.
Even though Manchester City managed to advance to the round of 16 as group winners after sweeping all matches with a win, they are actually experiencing a decline in performance. The player injury factor is the most reasonable reason, but a club as big as Manchester City should not be too dependent on just one or two players because they still have quality players who are ready to play in the areas needed.
Manchester City's performance in winning the UCL last season was very different from what they showed this season. With their current performance, I doubt they will be able to defend the UCL title for the second time in a row.