Napoli are really looking good, they are playing some exhilarating stuff and when needed are grinding out results. Their team spirit is equally high and with a good guide they should become a very stable force not only in Italy. Millan on the other hand are looking like they want to learn from their capitulation of last season. Verona were just dangerous in the opening stages of the matches and Napoli should be feeling lucky that Verona did not end their unbeaten run the way West Ham have ended Liverpool's. Napoli have only played 2 of the big 6 so far, they're yet to play Milan, Inter, Lazio, Atalanta. While Milan have played all the big 6 except Napoli and are still unbeaten and are on the same points. Napoli do not seem to last long in the first position.
That grinding out results part is the most important thing. I feel like when 11 players all get together and play their very best then there aren't that many teams that could stop them, sure the bottom table teams are not like that but most big teams are like that.
So, when you have a manager that really puts all the team into a shape and makes them play with 100% every single minute, you are going to get great results. Even teams like PSG sometimes just "have fun" or do not play with 100%, imagine players like messi, neymar, mbappe playing with their hearts out every single game, they would get tired easily but the results would be very different. So, Napoli is not the best roster in the league right now, but they are the most hard working talented team in the league and that is how they get their success as well, that is just what I believe root of their success comes from.