I a gree with you. Napoli played at home but they couldn't maximize their advantage in the first leg. As you said Napoli's game was not that good. But at that time Barcelona's performance was also not good but they managed to get 6 shots on target. They couldn't convert several opportunities into goals. But it will be different in the second leg because they play as hosts. Barcelona can also learn from the draw in the first leg. I bet Barcelona will win and will qualify for the next round.
Napoli isn't in a very good form currently and they aswell didn't play against a weak side either, so I didn't expect they would have an easy game or so but talking about them not been able to really maximize opportunity I think it's actually out of place because they obviously did their best as even Barcelona wasn't doing any much better than they were doing in that game.
Napoli and Barcelona have almost equal chance the second leg for qualifications so both teams can still get to qualify depending on the result/outcome of the game, but then I think an away goal for Barcelona is an advantage already because it may count of there bee need for it probably a draw and they are trying to ascertain a possible winner who could proceed to the next stage but if Napoli gets an away goal aswell ,they are going to be even and then either teams will need a goal to stay ahead of the other to be sure to qualify for the next stage of the league.