Why would you say that they don't have any rivals challenging them for the scudetto, I mean they literally almost lost the trophy to inter Milan who were actually the ones leading the league until they had some set backs in their play which really affected their gameplay and gave Napoli the upper hand and I believe this was even due to the fact that inter Milan attention was focus on two competition which is the champions league and the seria A, I think they do have an active contender for the title this season cause inter Milan can still do something.
It's normal that the boys were employed on multiple fronts, the fact of having a single team that puts all its resources into so many matches, means that the team then arrives tired and gets lost in the year as happened to Inter, now they need to find their form for next year