The presence of Rudiger can already complete the Real Madrid defense. Militao doesn't look very strong, but next season he will be starting to mature and is very suitable for a duet with Rudiger. Alaba could have been returned to his original position at left back. Tchouameni is Real Madrid's main target to regenerate the midfield, because in this position many players have started to age. Real Madrid also release a lot of old players, so it is imperative for them to find replacements to add depth to the squad. Maybe for the next season, Ancelotti can still rely on the existing squad.
I don't think Real Madrid's defense is weak last season. Their defense is stable enough. At the same time they have a great goalkeeper. Courtois is very talented. Real Madrid should strengthen their attack. In the last few seasons, they have relied only on Benzema. There is no guarantee that Benzema will be able to maintain his extraordinary form next season. At the same time, if midfielder Luka Modrich leaves, Madrid needs a proper replacement.