It's very difficult to predict a team's consistency, even though Napoli were successful in previous seasons. However, everything is different this season. We can't judge anything at the start of the season, only the overall strength that we can assess, and that's the benchmark for a team's ability to win the title this season. I think Juventus is much stronger this season, so they're worth considering.
In the next match, Juventus will face Inter Milan. I think it will be a testament to the strength of both teams. Inter Milan this season isn't as strong as last season after a change of coach. I think there's a good chance Juventus can win the match.
You are absolutely right that it is too early to judge team consistency and changes at both Juventus and Inter Milan make things very interesting this season. You also correctly noted that Inter has new coach Cristian Chivu who took over from Simone Inzaghi. Upcoming match between these two teams which will take place at Allianz Stadium in Turin will be crucial test for both sides. It will be great way to see how they have adapted and who has early advantage in title race just as you said.