Even though Napoli are not too bad this season, I don't think Rudi Garcia squad is at the level of Milan and Inter in many ways. Talking about Napoli, there is still a very good chance of winning Serie A again, but of course extra work and performance improvement is needed to be consistent to create a positive trend.
If Napoli wants to defend the league title then they need to improve their performance. I will actually say that only eight matches have been played and there is still a very long way to go in this season. So even though the start has not been ideal for them, they can still improve their performance and turn things around.
But they will have to be consistent and they will also have to win against big opponents. The performance that they have shown so far, does not indicate that they will be able to improve their performance quickly.
Another thing is, let's remember that the coach is new. So he will probably also need a little time to actually settle down with the club.