Have you forgotten that Napoli has a new coach this season, and yet they were able to win the Scudetto this season? So I believe Inter Milan signing a new coach won't stop them from winning the Scudetto next season if they play well. It is true that Napoli is serious in the transfer window, recruiting players to get ready for next season and possibly defend their title next season, but I still believe Inter Milan has been in good form in the Serie A league for years, and they have a good squad depth that can rival Napoli for the Scudetto next season.
As far as the team has a better squad and the new coach is an experienced coach, what will stop him from winning the main trophy for them? There are even a few examples of coaches who won their league in the first season they signed for a club. As you said, just look at Napoli's performances before Antonio Conte took over as the coach; but when he took over, in his first season, they won the Scudetto. Also, look at other leagues like the German Bundesliga: in his first season at Bayern Munich, Thomas Tuchel won the title.
I fully agree with you that Inter Milan getting another coach will not stop them from winning the Scudetto next season. The main reason why some people are not expecting much from the new coach is that it’s his first season. People tend to expect low performance if the coach doesn’t have much experience or doesn’t have a record of great success. However, if the coach has a good track record and is known to be experienced, people will expect him to win trophies in his first season.So, as far as Inter Milan has a great squad, I don’t think anything should stop them from competing for the Scudetto next season.