You think Flick didn't do much compared to what Xavi did but I think it's because Real Madrid didn't do well last season is why they made it out. If Real Madrid was really the way they are all this while? Believe me the way they were fighting and all others way to make it to be first team on the table, it would have been impossible for Barcelona to win Laliga last season but Real Madrid lost its 3 El clasico, there was nothing to show off about their performance.
I think what you said is true, besides comparing which one is the best between Flick and Xavi, there is Real Madrid who we know had a very bad performance last season, this is one of the reasons how Barcelona path to winning La Liga became a little easier, Barcelona took advantage of this opportunity very well, they performed consistently until they managed to lift the La Liga trophy.
If they are that fabulous and team think they have improve, they would have done everything to win the Champions League but look at Real Madrid mistake from beginning to the end of their season, they lack importance of defenders, they were losing too much that it was affecting everything they were doing. Not to forget about Mbape adaption in the team, his first two month was chaos, he was struggling to make goals, someone that was once the best in France. This is why I think Barcelona aren't that different.
The losing streak in El Clasico not only affects the standings, but also the mentality of the champions, the mentality of the players is tested here. Another important thing is the defense, the fragile defense is one of the causes of Real Madrid defeat in previous matches, the opposing team relentless attacks cannot be resisted by the defenders available and when it comes to Mbappe, of course the player is still in the adaptation phase in the team, plus the excessive expectations of him have a psychological impact.