It is true, Real Madrid didn't release all their main players in that match, while Barcelona played with full key players. Actually, it's an unequal match, Real Madrid seems not really serious to play against Barcelona. Ancellotti may just focus on giving the new players time to play against a strong team. He also wants to know the quality of the substitution players. Based on this matter, surely this match doesn't determine anything. We cannot judge Barcelona already stronger because they can beat Real Madrid by scoring a single goal only.
Pre-season cannot be an illustration for the next game. I haven't felt any concerns about the players madrid have for next season. They are still capable enough to compete with other teams. Modric, kroos, and Casemiro continue to be Anceloti's top choices. They became the heart of Madrid's game.
Indeed these three players are seniors, anceloti has a tough task if the three of them retire. I hope Anceloti will not be late looking for players so that the champion generation continues and does not make mistakes like Barcelona.