So, you're saying both teams have a 50/50 chance of winning the match. That's not wrong because until one scores, it's not obvious that Madrid will win. Dortmund isn't at Madrid's level, but Madrid should never underestimate them. However, we know that Madrid never disappoints, especially in finals. Atalanta surprised many people last week, but I don't see the same happening here at Champions League. Will Dortmund end the monopoly? I dare to say yes because experience matters most at this high stage, and Madrid has that all the way.
When everything is decided in one match, then perhaps you are right when you say that the teams have equal chances. If they were able to reach the finals, then they are strong enough to do it. The recent match when City failed to achieve victory in the final is an example of how a clear favorite can lose, a few good attacks, some kind of mistake, a good defensive game, and the outcome becomes completely unexpected.