It is not as easy as you are saying it even though Real Madrid has more champions league experience than Arsenal, if you check Real Madrid last two matches you will notice a slack from them and I don't really know what is the course, or will it be the champions league that makes them slack and lose last match. The only hope arsenal have in this season is this champion league and Real Madrid still have hope in the Copa dey Ray they will be playing with Barcelona and so Arsenal will play with all there might to make sure they have a good result so it is going to be a strong one and so lets not jump into conclusion that Real will beat Arsenal.
I don't think it's about jumping to conclusions about one team because if we look at both teams, you yourself don't have to jump to conclusions from Real Madrid's sluggish performance in the domestic league in their last two games. Because it's possible that Real Madrid will bounce back when they play in the Champions League, especially if the Champions League is a league with a much higher caste so it will be considered a much more important competition by any team including Real Madrid who are often successful in the Champions League.