On paper, Napoli and Inter Milan are strong contenders for next season Scudetto, but Juventus and AC Milan also have a tradition of challenging for the title every season. While Napoli and Inter Milan do have better squad depth than the other contenders, that won't be the only determining factor in their success next season.
Inter Milan may not be as strong as last season, having parted ways with Simone Inzaghi, and Chivu will certainly need some time to adapt. This could be beneficial for Napoli, making their defense of the Scudetto a little easier. De Bruyne is an excellent signing, his presence in the first team squad will have an immediate impact on Napoli performance, both in Serie A and the Champions League.
I would say that among the squads of Serie A, Inter milan and Napoli are the strongest. Anyhow , it is difficult to say how Inter Milan will perform with the help of a new coach. Inter milan's performance is likely to decline with a new coach. But Milan's squad is quite strong.
Napoli have added Beukema and Noa lang to their squad but the most important thing is that napoli have got an experienced midfielder like De bruyne on a free transfer. If De Bruyne does not face injury , he will play an important role in stabilizing Napoli's overall performance...
On the other hand , we have seen better performance from ac milan in the pre- season matches. In addition , the team will not perform in the Champions league or the Europa League. So the team has the potential to do well in Serie A. But Milan's biggest weakness is that they cannot continue their good performance.