I think you have a point, especially since Xavi manages Barcelona. Xavi understands what his team needs to win El Clasico and that has inspired the team to win it more often. The first El Clasico match was played at Barcelona's home ground, that's something that might give them the lead even though it's still possible that Barcelona won't be able to play all their best players.
Real Madrid is dangerous not because of Bellingham and Vinicius, but players like Valverde and Kross can also have a positive impact on the game. But before the El Clasico match, Real Madrid and Barcelona will play two other matches in two different competitions. Player rotation is expected and may be considered, which is a good thing ahead of El Clasico.
For now it is actually not too wrong to discuss El Clasico from the beginning with several possibilities that occur but when time is approaching there are still some things that need to be considered because after the league is off the international break Madrid will have 3 matches within 8 days starting from facing Sevilla, Braga in the Champions League and Barcelona in El Clasico and the problem is Barcelona has a fairly minimal break because looking at the schedule they will do because they can only rest 1 to 2 days because they have a schedule of 3 matches within 3 days against Bilbao, Shakhtar and also Madrid.
Obviously the vulnerable time is quite short in resting after this match will create a condition where players will be forced to continue playing and this will actually be very dangerous because in the end fatigue can be one of the triggers for players not to be optimal and even injured.
Therefore, before El Clasico it would be better for Ancelotti and Xavi to think about how the right rotation to face a busy schedule but the players are not burdened and too short because this could hamper their condition in the game.