In football with 2 legs, we have seen too often in many recent years that even 4 goals is not impossible to overturn. Barcelona did it many times, and of course themselves were victims. Remember PSG was a victim of it and even City themselves will remember how my team turned everything around in second leg:)
Of course, in Football there's always a possibility of a comeback, especially when the match stretches across two legs, that's unarguable, but the point is that City have the advantage, and PSG need to score at least two goals and pray City don't score at all, so they can qualify, that's definitely not beyond them, but it's difficult to pull of. We'll see which team goes through, and most likely it'll be City, after moving within just three points of the EPL, they'll know that one is all but over, now it's time to become champions of Europe.
But yes, City is enjoying this position and the red card for PSG means they have a weaker side fielded.
Gana is a very important player for the French Champions and he'll be a big miss, Herrera I think will fill in for him, he'll have a very difficult night against the likes of KDB, Foden and the rest I'm sure.