Why are you then saying that the new players will surpass the performances of the former ones when in the next sentence you write that Dembele is almost the same as Neymar? Which is actually true because Dembele is as susceptible to massive injuries as Neymar and misses most of the games. You can check his injury history and will see that substituting Neymar with Dembele is really risky because it could be exactly the same problem. Replacing Messi is impossible as well or who do you think will play as efficient as Messi did?
Individually Dembele is very far from Neymar and Messi, but in contributing to PSG it is possible that Dembele can surpass Neymar if he has a long tenure at PSG. But this is just the start of the season, if Dembele and Mbappe can avoid injuries, they can make a good contribution to PSG.
Yesterday's draw will motivate Luis Enrique's squad in the second week, Mbappe is reported to be starting tomorrow's match, a worthy duo later.
I don't think that Dembele will surpass Neymar. The problem with Neymar has never been about his statistics. It was about his injuries. In fact his statistics are pretty good when you look at the games played and the assists he gave and the number of goals he scored. I don't think that Dembele will be any better than that as he has never been a really good scorer anyway.