I really have no idea how Real Madrid won this El Clasico by 4-0 away. It was a Copa del Rey game maybe but both teams were caring about the cup anyway.
Regardless of whether the trophy is important or not, this is once again prestige. Madrid had given up the previous Supercopa cup and most likely La Liga would be the same, when this is given back then Madrid will obviously lose face so now with this win at least Madrid's chance to bring the trophy this season is still maintained even if it's only the Copa Del Rey trophy.