besides the problem in the defense line, I think the transition when attacking to defending that Napoli implemented was not successful. there was a delay in filling the gaps left when they tried to attack. while they also had problems in finishing.
Conte has a lot of work to do in the Napoli team. it will take time and will not happen in a short time. replacing some players may be a short-term solution, but the coordination of the game between players must be trained much longer.
Obviously conte is yet to get it right with Napoli of which is normal, even Chelsea who has their coach changed are also suffering similar thing, I will want to believe it's just the beginning of the season and so they should be given some more time, just maybe they will do better than they have been doing, Napoli's defense line has got some adjustments to make and the fact they they are not having a firm attack to will burden the defense or maybe is a tactical problem, whichever it is I hope conte gets it fixed soonest least they end up the same way they did last season.