Yes you are right it is hard to know which team will be best in Serie A next season. Teams like Napoli and Inter Milan have had good and bad years. Now many top teams have new coaches which makes it even harder to predict. But we know that Napoli hiring Conte is big deal. He is great coach who has won many championships in Serie A. I also think he will make Napoli strong team again and maybe even lead them to another championship. He is good at motivating players and making smart decisions so I would not be surprised if Napoli does very well next season.
I also hope that there can be several teams that become strong next season in Serie A and also including teams like Napoli and others because with several new coaches filling the big teams in Serie A, of course it will make Serie A more interesting to watch because the competition could be even fiercer than last season. In addition, I also hope that the teams that were previously slumped in Serie A can rise better like AS Roma and also Napoli who will be trained well by Conte next season.