You have to go with the bookies and then you say you go with Real Madrid, but the bookies see Arsenal as the favorite.
You think they have been a good team two seasons ago and it is true that they had more points by the same time of the season, but they stil have only lost three games this season so far in the Premier League and you should take into account that they are so far behind Liverpool, that I think they have given up on that title a while ago. Like not entirely given up, but they were being realistic about it.
But by no means would I underestimate them in the Champions League. There is no reason to do so. When the second from the Premier League is your opponent, everyone knows it is gonna be hard.
Arsenal is the favorite for Bookmakers in the match against Real today, but I would not rate the teams too much based on the odds today. I admit that Arsenal can play a good match and beat Real, but for now I am looking at the bet Real will not lose for 1.7, or Real total over 1 for odds of 1.83. But I will bet live, I think that there will be no quick goal and in live I will be able to catch much better odds. I think that Real will not lose today, Real with a handicap (0) for 2.58 also looks tempting, but I will not rush, if Real concede first I will bet on them + handicap.