In the first match, it was Barcelona who got the advantage in Italy. The rematch will be in Spain, so I think Barcelona will be the team that will take the advantage. Napoli will have a difficult away game. The strengths of the two teams are very close to each other. That's why I can say that it will be a difficult match to predict. It will be such a match that both teams can win. Maybe it will go to penalties and the penalties will decide the team that will advance to the next round.
The strength of both team are relatively close to equal like you did rightly mentioned a d I'm not in any way doubting that because I've seen that even in squad depth, Napoli has got a good dept aswell which can not be seen any less when compared to that which Barcelona has got. I think I wouldn't be wrong to say in their last encounter Barcelona was lucky to have taken the lead ahead of Napoli.
In this second encounter which will be in Spain it's actually going to be really tough like you have rightly speculated because Barcelona wouldn't want an embarrassment on their home geoud and Napoli also wouldn't want to end their champions league journey at this point so it's really going to be a fierce battle between both teams as they will struggle to move onto the next stage, it's going to be a determinate game hence the battle wouldn't be for the weak but for the best team amongst them both, in your words it's looking like Napoli has got an advantage due to the presence of osimhen but then Napoli hasn't had really good results outside Italy.
I'm not going to allow myself into the pressure of putting so much of my support on any of both teams but I will just watch and enjoy the game as I know I'm expecting to watch an exciting game which will determine whose going to the next stage of the UCL and the action that comes with the UCL causes one to want to stay glued because especially games like this every minute will actually count.