Juventus lost their key player Ronaldo, and their squad won't be as strong as it was. Napoli have been doing pretty good this season, winning their last two matches, and they won't can to lose their next match. Napoli's last meeting against Juventus wasn't a successful one for them, they lost the game with a 2-1 score, and Ronaldo scored the first goal. However, Juventus can still do better without the presence of Ronaldo. They just have to work hard.
Allegri is a genius coach, he can turn a Milan full of old players into Serie A champions, while the current Juventus players, are still much better with Milan's conditions at that time. So, I think, even without Ronaldo, and Pogba's plan to Juventus didn't happen, with Allegri's ability as a coach, I think they still deserve to be favorites to win. It is true that it will be more difficult, but at least Juventus still benefits from the condition of their competitors such as Inter, Milan, Lazio which are in less than optimal conditions as well. Against Napoli, because this is a game that the team need to adapt without Ronaldo, holding Napoli with draw is not bad result IMO.