I have a slightly different opinion than you. I think the Barca and Napoli pair is quite unpredictable; they are the reigning champions of both the Spanish and Italian leagues. Currently, the form of both Barca and Napoli is not good, but when they face each other, the result is hard to predict. Napoli's style of play remains challenging for teams from England and Spain. Therefore, it's not easy for Barca to overcome Napoli in this round.
When you look at the performance of this two teams, it is very obvious that they are on the same level now. Their individual performance in both leagues is just the same and nothing much can be said in their upcoming match against each other. One of this two teams will be eliminated from this round and won’t advance to the quarterfinals, the thought of it makes it more interesting to watch out for their match by next year when they meet in the round of 16.
Barcelona is currently not in a good situation, otherwise, a team like Napoli could never beat Barcelona with the performance they had during the last season with their coach Xavi, but since there are many injured players in this team and there are many players who left the team, I think this can be hard as you said to predict this match.
I think Napoli can have a good chance to score a goal in this game if they have Osimhen in the good form because the defenders of Barcelona have not performed well recently.
Barcelona are a bit off form right now it's true. However, I think Barcelona can do well against Napoli. Because the performance of the Napoli team is not good this season. They are not able to dominate in Serie A. The team has won only 8 out of 16 matches in Serie A. If they are in good form like they were last season I would definitely consider Napoli favorites against Barcelona. But since the performance of Napoli players is also completely erratic. Especially the team's defense is quite weak. For these reasons, I will call Barcelona the favorite for this match. Barcelona's squad looks stronger than Napoli's to me.