Inter Milan is one of the strongest teams in Serie A, and their performance in domestic competitions is undeniable based on their results. Last season, they missed out on a trophy because Napoli were much more focused and much better. This season, Napoli is much stronger because they have managed to bring in several experienced players, and I think it will be very difficult for Inter Milan to compete with them.
In the last five seasons or a little longer, Inter Milan are a strongest club in Serie A with Scudetto titles they won and general performances in other seasons as well as in UEFA Champions League. They are a best representative of Serie A in Champions League and it means many thing about their strength. AC Milan and Napoli won Scudetto titles too but they have not reached to quality level of Inter Milan in latest seasons.
No one knows for sure because every team fighting for trophies will do everything they can. Inter Milan is still a title contender next season, but they need to make significant changes, otherwise Napoli will still be a strong candidate.
Napoli will have good chance to defend their Scudetto title with uncertain performances of Inter Milan with their new, young and inexperienced head coach like Chivu. However, Napoli have possible big problems with their limited player resource and an injury of Lukaku before their first match in Serie A is an example. Napoli have less star players than Inter Milan and likely have bigger issues if key players injured.