You have said it all, Luck is what is always on Madrid side. In the group stage, they will struggle to survive and after qualifying to the round of 16, they will start playing in their best performance joined with luck, gives them a upper hand over every other club in UCL. I am expecting to see them in the finals, because it's certain that they will be in the semifinals.
I disagree with this a bit. You can win "one" match with luck, maybe even two. But you can't win the title by luck, because it requires so many games to get there. You first play 8 games at the group stages, depending on your result you either finish within first eight, or you finish outside and play 2 more games.
You play last sixteen, you play quarter finals and you play semi finals, all of them from two games six more games. Then you have final game that you have to win. So by logic, you have 15-17 games that you need to play and while a few of them could be based on luck, not all of them could be based on luck. Real Madrid could get lucky and win against a team, but they can't get lucky and win the title by pure luck.
Is there such thing as luck in football?, well, that I can not tell. But one thing that I know for sure is that the team that takes/capitalize on their chances ends up winning the game.
Check the last two champion's league that Madrid won. They where not even the best team across Europe that season, but just because they have a very brilliant attack that knows how to put the ball at the back of the net no matter how difficult it is, they where able to secure the trophy.
Take Manchester city for example, in their treble season. They where not the team with the best defense in Europe, but they ended up winning the treble. Why is that?, because they understand that scoring the necessary/important goals gives you a point or win you something. That's why when you see Manchester City conceding 3 goals in a game, then you should know that they've also scored more than 3 goals to win that game. That's the logic. Score more goals than your opponent to win your game. And that has also been the madrid's pattern. As long as they are still in the competition, they will continue to fight until they get more goals than you even if it's just by a margin.