Having lost a pre-season game against Barcelona I was a little bit nervous. But that result cannot be the benchmark for the League's start. I think anceloti has considered all. They have a lot of old players, but their physical strength is still able to compete. I think that's what makes Anceloti not looking for many new players.
Madrid still have a chance of winning, even if they are old. But for the observers perhaps Barca are potential champions because they buy a lot of new players. Perhaps Anceloti does not want to be like other coaches who make star players fail to develop.
Their physical strength will not always be able to compete, I think the experience that some old Real Madrid players have is much more likely to beat the younger ones.
Ancelotti can probably hope that Barcelona cannot sign all of his new players for the season and that will make little difference to their strength. Barcelona are reportedly still struggling to register 5 new players, but they will have to wait for some player sales before resolving this issue. I think they still have options if no one really wants to leave, but it should be the last resort.