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.
I think that Barcelona just now look a bit worse than Napoli in terms of their physicality, so you can make even a slight bias in favour of a Napoli win. But since there will be two matches, it's hard to say exactly how the 1/8 will end. Both teams know how to get back on track