It's not just about knowing someone's weakness but also knowing who will be available at the time of the encounter. Ancelotti may have the best strategy in place but he doesn't have the required players to execute it perfectly due to injuries.
When Ancelotti has decided not to bring in many players in the transfer season it means he is ready with the players he has and it is certain that he has the players to execute the scheme that Ancelotti wants to do with the players he currently has. And indeed it can be proven by their impressive appearance this season with several formation schemes carried out for alternatives to keep the situation good.
Indeed, for the problem of availability due to injury it is another situation that we cannot do much but with several injured players such as Courtois, Alaba and Militao to date I do not think it is an obstacle because even though in a match Madrid always plays with players who are positioned not according to their comfortable position but it still runs very smoothly for them. Likewise in the match against Manchester City later because it would be ridiculous if they are still questioning the availability of current players even though they have performed well with the same players this season.