Despite the fact that Barcelona were beaten by Jude Bellingham's late goal in their game against Real Madrid last weekend, I don't think it should make anyone to think that the club is now underperforming because before the commencement of that game, Barcelona were still unbeaten in the Spanish La Liga.
Real Madrid is one of the best clubs not just in Spain but the whole of Europe and has the capability and capacity to beat any side in the league. So losing against them on Saturday shouldn't make anyone think that they aren't good enough to compete for the league and European titles again.
I agree with you, defeat against Madrid is not the end of everything for Barcelona, either in La Liga or in the Champions League. Madrid and Barcelona have both suffered one defeat so far, and currently Ancelotti squad is temporarily leading the standings, and there is no guarantee that they will be unbeaten in the future. On the one hand, Xavi had to admit that Ancelotti squad was superior to him, Bellingham was able to make the difference which made them lose three points. But what is clear is that there are still many matches ahead, they must shift their focus to the next match.
On the other hand, the top four in the La Liga standings are occupied by newcomers Girona, with the scenario of beating other weak teams, they managed to collect the same number of points as Madrid, leaving ATM and Barcelona behind. Who would have thought that they have very good statistics, if Madrid is careless then they will lead the top of the standings.