If Napoli beats Red Star, a draw at PSG wouldn't change anything apart from the fact that we can win with one goal difference at home instead of two.
That's a big difference though. As I said, every team you've beaten by more than one goal this season currently sit 13th or below in the league, or are Red Star. There's also the mental difference of going into your final game off the back of a draw in Paris, knowing any win at home sends you through, and going into your final game off the back of a defeat in Paris, knowing that even if you're winning 2-0 in the 90th minute, a stoppage time goal for Napoli still sends you out.
We have to beat Napoli by more than one goal & we're through regardless of what happens in all the other games.
Firstly, on current form, you aren't beating Napoli by more than one goal. Secondly, there's a huge difference going into your final game after a decent away draw, needing any win, and going into your final game knowing that you have to win by a certain number of goals.
In your last eight CL games you've conceded 13 goals and kept just one clean sheet, and that was at home to Red Star. This "win by more than one goal and we're through" thing is not as remotely straightforward as you're making it sound, and I think drawing at PSG or Napoli slipping up against Red Star is the difference maker you'll need.