Real Madrid is simply the best team for the Champions League and that's why they are the absolute favorites for the title every year. A lot of unexpected things would have to happen for Dortmund to see them as winners, but nobody expected Leverkusen to lose in the EL either and Atalanta still managed it, so why shouldn't Dortmund also not manage it?
True. Real Madrid is always the favorite team to win UCL every season. People even call Real Madrid as the king of UCL, no team can achieve the same thing like Real Madrid. But Dortmund, this is a surprising team, no one favor Dortmund to reach the final. In the early of the season, most people expect to see Real Madrid vs Man City in the final match. Unfortunately, Real Madrid must face Man City in the quarter final. So, people assume which team can win in that match, they probably become the winner of UCL this season. Luckily Real Madrid can defeat Man City, now Real Madrid is the only favorite team.
Yes, we must be aware that the miracle sometimes can happen. The result of the final match in Europa league is the real example. We can't deny that it also can happen in UCL final although it should be smaller chance. The capability of Leverkusen and Real Madrid is very different, Real Madrid is like the king of the tournament but Leverkusen becomes a stronger team in this season only. Leverkusen surely doesn't prove anything!!!