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.
For the first few weeks, Juventus, AC Milan, AS Roma and some other contestants will probably be competing closely with Napoli and Inter Milan in the race for the Scudetto. Napoli seems to be stronger among the other contestants because Conte is staying, besides they are also actively adding strength by recruiting experienced players like De Bruyne. However, let's see first how other Serie A contestants complete their plans in the transfer market, as you said, it can be a reference to assess how ready they are all to face the challenges in the next season. Inter Milan don't seem to be as strong as last season, as they have parted ways with Simone Inzaghi.
When a team that is having good results changes coach, that team takes a lot of risks. The new coach may not be able to perform well, and the fans will put a lot of pressure on him. I think it will be very difficult for the new Inter coach to achieve the same feats or surpass the old Inter coach.
Regarding Juventus, I don't expect great things, nor do I expect great things from Milan. Now, regarding Roma, if they had continued with the same coach, they would probably have been able to win a place in the European Champions League. With this current coach, I have some doubts.