In order for Arteta to be perceived as a good coach, he needs a big win, beating Real in the Champions League would be a great step for this, but everyone has big doubts about this. Real is stronger in players and Ancelotti has much more experience in the Champions League, which of course plays a huge role at the playoff stage, where even one mistake can decide the outcome. It seems to me that Arteta will have another season without trophies.
If they want to be a big club they have to be able to chase the Champions League trophy and that is not an easy achievement because they have to face a tough team and have quite a lot of experience in the Champions League. Arsenal's chances are small because there are no opportunities that they can get, unlike when facing other teams. But even so they can fight and can determine their steps if they manage to beat Real Madrid.
There is no need to think about the quality, experience or mentality of Real Madrid players because all Arteta needs to do is win the match in the first leg. If that is done then Arsenal have hope to be further in the title race even though it looks a little more difficult.