The main problem with predicting this match is that both Barcelona and Napoli have erratic performances. It is impossible to say which team will play better in which match. We have seen several times this season that Barcelona have dropped points even against relatively weak teams.
However, compared to Napoli, everyone is keeping the Barcelona team ahead in this match. Barcelona's overall performance is better than Napoli's. Even Barcelona's squad is stronger than Napoli's. Moreover, Barcelona's overall performance was better than Napoli in the first leg match. This is the reason why Barcelona team is considered as the favorite in the second leg home match of Barcelona.
Barcelona will act as hosts in the second leg, this is one of the factors why Barcelona deserves to be favored over Napoli. It's true that Barcelona as a whole posted better statistics, Napoli experienced setbacks and had to change coaches twice this season. Even though Xavi plans to stop at the end of the season, he is determined to take Barcelona further in the Champions League this season. Apart from that, in their last match Napoli drew, while Barcelona managed to win.
The match between Barcelona versus Napoli is difficult to predict, because Barcelona not too dominant over Napoli. However, Barcelona has more complete attributes than Napoli, such as a more even squad depth and a better reputation. It could be that Napoli managed to get rid of Barcelona, but on paper Barcelona is the right favorite. Everything will be proven in the second leg, betting on their victory seems very risky.