Barcelona is currently below the other European teams in my opinion, they can give a lot and players like Yamal can make the difference but we need to see how the coach decides to let them play, it's a very difficult thing to understand due to all the players available
Why do you assume Barcelona is below other European teams? Barcelona has quality players, Yamal is just one of the key players of Barcelona. Yamal is a very young player but he could contribute much for Barcelona. Although Yamal has no much experience in UCL, Yamal has a very explosive power. Whenever he is in Barcelona lineup, he very often showed the difference. Moreover, Barcelona has Lewandowski who is very experience in UCL. Lewandowski could be the player that possibly brings the change in the match, too. With these great players, it is quite strange that you assume Barcelona is in the lower level compared with other teams. 
It is true that Real Madrid has good squad depth and also in Real Madrid there are many star players which will definitely make Real Madrid the favorite in the next match and I personally also have hunch that Real Madrid will definitely be able to make Dortmund lose in that match.
No doubt Real Madrid has many star players but many of them are injured now. Meanwhile there are 3 Dortmund players only who got injured. In this situation, Dortmund has the advantage because they can easily determine the lineup. It is very different with Real Madrid, they will be difficult to determine the lineup because they lose some key players. In this situation, I'm not sure that Real Madrid will beat Dortmund.