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.
I think Napoli without Spalletti will not be able to go further in the Champions League this season. Napoli faced a big obstacle in the round of 16 because Barcelona is not a weak team even though they have not been in good form recently, but in the Champions League, Barcelona performance is certainly much better compared to the domestic league. This match will be a life and death match for Napoli in the first leg because if they fail to get a win at home then they have no hope of beating Barcelona at Camp Nou.
Barcelona wants to record a new history under Xavi coaching so they will try their best to beat Napoli in the round of 16. Napoli don't even have any hope of winning the title this season because in Serie A they are far behind Inter Milan and also in the Champions League they have quite a big obstacle in the round of 16.