Juventus is still powerful against napoli even without Ronaldo. When check statistics, except for the match played in last Februry when Napoli won, Napoli didn't win any match against Juventus since 2018.
Juventus didn't do well during the last two matches, but i think it still can compete with Napoli to get a good standing among the first five top clubs; it lost against Empoli [0:1] and a draw with Udinese [2:2] which i think are not a very rud results compared to Napoli who won the last two matches against two weak teams Venezia and Genoa which have less standings than Juventus .
Historical results tends to play very little role in future fixtures if the team that has been dominant in past years now have degraded performances and that something we've seen in this current Juventus team. The last two games have shown that even if they have a rich squad, overall team output and performance is generally bad if not their worst in recent years. That's why if Napoli do just enough to keep Juve's attacks at bay, they would have a clear shot at winning the match.