Most likely Juventus and AC Milan will wait for the moment from the 4 clubs, expecting all four to experience defeat or make mistakes in several important matches and later it will be utilized by Juventus and AC Milan, but even so the result of the Juventus versus AC Milan match indicates that the match really expects a draw from these two big clubs, even so Atalanta, Inter Milan, Fiorentina and Lazio, are still considered tough but of these 4 clubs the one that stands out is Atalanta compared to other big clubs, because consistently in every match Atalanta, Fiorentina, Lazio always get a good win so that's why Napoli's current competitor is not Inter Milan but these 3 clubs who are likely to win the Serie A title this season.
All the clubs on the second to fourth positions are threat to Napoli and don't also forget that Inter know how to stay strong for so long, and they are always among the title contenders from season to season. I know that Fiorentina and Atalanta are fully in form but it's for them to continue in this great form till the end is what no one knows if it will be possible or not. As for Lazio, I don't see them lasting long on top of the table. This season is not easy for Napoli like last two season that they won the title for the first time.
Serie A has been running for 13 weeks and so far it is still very competitive especially in the first to sixth positions. I also agree with you in the end big teams like Napoli, Inter, and Juventus can compete until the end of the season. Teams like Fiorentina, Lazio, and Atalanta have been very impressive so far, but I also have a little doubt that these teams can continue to be consistent until the end of the season even though in football anything can happen but it seems difficult.
In addition, if I predict the chances of which team will be able to win the trophy this season, I will favor Napoli over Inter Milan. The reason is, Napoli is trained by a coach who is very experienced in maintaining the consistency of his team and he is also a specialist in winning titles. On the other hand, because Napoli has the advantage because they don't have many games to play, this is different when compared to their rivals who play in the Champions League. So of course their concentration will be divided, but not for Napoli, they only concentrate on Serie A.