Real Madrid really deserved the victory, because they didn't allowed Barcelona to score a single goal from the match to prove to people that the injuries some of their players had some months ago that affected some of their potential players not to performed well that gave Barcelona to defeated them 2-1 in the first leg. Real Madrid were able to used all their potential players to played the second leg to defeated Barcelona 4-0 which is a sign that Real Madrid may have something reasonable to achieve in this tournament. Barcelona performance was very poor in this second leg which their coach need to apply some skills that will improve their performance in their remaining matches.
One thing i understand about El Classico is that expect anything. There is nothing like home or away. The come back in the second Leg at Camp Nou proved so many things. It was almost the same sets of players in the firs t leg of the Copa Del Rey. The only change was the formation and starting Rordrygo and sending F Valverde to Midfield which i don't see as excuse for Barcelona losing such amount of goals. But this is El Classico where anything is possible.