Playing only the championship is certainly an advantage for Napoli, it can better manage the forces, unlike the Inter which is still engaged in all competitions and therefore the drop in performance can be there. If Napoli really wants to win the Scudetto, he must know how to manage the strength and results well, so far he has also been lucky on this point
Yes, this is indeed a special advantage for Napoli, because in terms of schedule they do not have a tighter schedule compared to their opponents in Serie A. They can take advantage of that, not to save strength, but their strength can be maximized for them to show in Serie A. However, that is also not a guarantee, because in any case there are many factors that influence a club to be able to play well. It is not uncommon for clubs with tighter schedules to be able to play better than clubs that are not physically more tired.