For the closest competing teams, of course Juventus, Inter Milan or AC Milan will disrupt Napoli's progress in defending the title. However, I see AC Milan has a greater chance because AC Milan will not compete in Europe next season so their focus is only on Serie A. Moreover, with the arrival of a new coach who will make them able to change their course to be better to compete again at the top of the standings.
Milan has a good squad, unfortunately their biggest problem last season was their weak defense, in my opinion they were doing very well in attack, in most games they managed to score at least 2 goals. Now with the arrival of Massimiliano Allegri, I believe that Milan's style will become stronger in defense, I just hope that Massimiliano Allegri doesn't make Milan's attack weak
If Massimiliano Allegri can strengthen the defense, which is his strong point as a coach, but maintain Milan's good attack, then I predict that Milan will be able to achieve good results, I don't really believe that they will be able to be champions, but they can get second or third place.
You are right that last season it was quite obvious that their back line was considered quite weak, while for the front line I think that their front line is not as good as what you think, because goals are more often created from the midfield compared to the front line. In the middle of the season they started trying to fix it by bringing in Joao Felix from Chelsea, for the initial debut with AC Milan Felix performed quite well, but the rest he returned to being a blunt striker, where in 15 matches he was only able to score 2 goals.
Last season the midfield of Acc Milan performed very well, and one of the key players was Tijjani Reinders, and something I never thought was that in this season's transfer market they chose to sell the player to Manchester City, even though he was a player who was quite promising for the future of AC Milan.