Napoli must be aware of how tight the competition is between other teams next season, not only in the Champions League, which certainly has strong teams. Even in Serie A, other teams are also preparing to strengthen their teams. Of course, Napoli will prepare their team for the competition next season. That's what they showed by being quite active in the transfer market this time. They are not only satisfied with their achievements last season.
When Napoli win the Serie A title then their target will increase to the Champions League that's why they are active in the transfer window this season, if Napoli just want to compete in Serie A I think the current squad is capable. I am not underestimating other teams but from what we see at the moment it seems that other teams are not so active in bringing in new players to face the new season, I know Juventus, Roma and some other teams are looking new players but so far there has been no significant movement.
For next season I still favor Napoli and Inter Milan but a little doubtful about Inter Milan regarding the issue of fixed matches. Do you see potential for other teams to catch up to these two teams? in my personal opinion, there aren't any yet, because I use the transfer window as a reference.