I think, losing Dembele and Ansu Fati also contributes to the decrease of Barcelona performance. I still remember that these players often give the difference when they played in big matches in the previous season. I am a bit confused why Xavi doesn't need them anymore. Xavi may not know that losing them will bring a big impact.
Regardless from this defeat, Barcelona also still has a chance to retain the La Liga trophy, the difference in points is not too big and it is still reasonable to catch up in the following weeks. On the other hand, Madrid is in top form at the moment, so it's not easy to beat them, especially with a player like Bellingham.
Bellingham is the man of the match as he made proper use of his opportunities to make sure that Real Madrid won the match. He is such an outstanding player that came not quite long and scored the two goals that made Real Madrid to see themselves better than Barcelona. He also scored in his first El Classico, in fact it was a great week for Bellingham, as he also scored in last week UCL.