I'm surprised that after endless posts complaining about defense you have settled on Ozil as a potential issue. Particularly as he was not playing for a huge portion of the disaster that has unfolded as Emery's reign as manager.
Personally, I am shocked that we ended up with Sokratis and Luiz as CBs. These are two of the most passive defenders in the world. We need to be more aggressive in defense, and I don't mean just pressing up the field. But I also think we have a problem retaining possession. We are winning the ball, but we give it away far too easily and cannot beat the opposition press and without Ozil, it is always worse.
We make the field far too big when the opposition are attacking. If you go here
https://www.whoscored.com/Matches/1376055/Live/England-Premier-League-2019-2020-Arsenal-Brighton, and mark the heat map of just the 4 defenders from both teams, see where our defense spent it's time, and see where Brighton's defense spent the game. This is why our defense has problems. They are playing far too deep.