PSG just have better quality but Arsenal aren't playing badly. Their problem in this game is basically a sign of what their season has been. All smoke, no fire. They really lack adequate quality up front.
They missed a critical piece of their midfield puzzle in Partey and PSG took advantage of it by allowing Dembele to drop very deep. With Odegaard being who he is, it was easy to play through Arsenal's midfield tonight.
Attacking wise they're the weakest. Defense they're probably the best after Inter. At this stage of any knockout competition, defending is what gets you through.