Kevin De Bruyne is a player with very accurate passing skills, and Serie A's tempo is a bit slower than the Premier League, so it's highly likely that Kevin De Bruyne will be able to contribute significantly to his new team.
However, injuries are unpredictable; even a player can suffer an injury in training. This is something that cannot be predicted, and hopefully, De Bruyne can avoid it so he can return to his peak performance.
Napoli's first match of the season will certainly not be easy. The team's strength in the first week is undeniable, but I'm very optimistic that Napoli can overcome it. Their performance has been excellent since last season, leading to their title win. Now, Conte has made several additions to make the team even stronger.
I would say while it is true that he will help a lot more. It is also important to remember that he is getting older and his body isn't as well as he used to be. When I say "older" people keep defending and say "but Ronaldo is 40 years old and still playing awesome?" well do you think KDB and Ronaldo has the same body?
KDB never was a runner, or go back on defense to help kind of guy, and City had a great system of playing that allowed KDB not to help out on defense too much. Napoli may not be able to afford that, it's going to be quite obvious that they are going to end up with much more issues on defense when he doesn't go to help. He will be the perfect registrar, but without anything further, they are not going to end up getting much help, just good passing, that's it. That's a huge problem when it comes to defense.