I make reference to current performance and form in their respective domestic Leagues this season and even last season because we all know how difficult Real Madrid is finding it to win matches back then when some of their players were injured.
Making reference to Champions League, I made it clear that Real Madrid is the most experienced team in the Champions league history, but still at that they are yet to beat Arsenal in the Champions League even though they met in some limited time.
yes I now that Arsenal are yet to win any EUROPEAN trophy but that is not related to my discussion because I am saying the fact based on history of the matches Arsenal and Real Madrid have played together.
I would guess that it is not about the group stages but more about the later on. Injuries play a big role in that, because if a team is missing an important player in the later stages that could be the decision maker for the match.
For example, City lost Kevin De Bruyne as we all know, but it is expected that he would make a comeback until later stages, but for some reason he can't, then it would be hard for them to win it this year, I would expect them to lose without a doubt. Doesn't mean that they have to lose, just means that it would be very hard for them to get the title. Same goes Real, they recently got Vini Jr. back if I am not wrong, but if they lose him again or anyone important, it would be hard for them to win as well.