Real Madrid already has the best players in it even though they are reserve players, Carlo Ancelotti does this so that he has lots of choices because if there is an injury storm like last season he doesn't need to worry because he is very good at rotating players.
I think that even though Real Madrid recruited a lot of players, they didn't spend much on their budget because they got Mbappe for free, at least 150 million euros he could spend on other players who certainly have good potential.
Real Madrid has been known to be quite clever in recruiting the players they want so far, so that the team's strength always looks more stable every season. Apart from that, what you say is also true in that Carlo Ancelotti is also quite clever in managing the main players with reserve players so that Real Madrid does not face excessive difficulties when several players suffer injuries before the season ends. This means that Carlo Ancelotti at Real Madrid can implement quite effective strategies, so it is not surprising that Real Madrid continues to be taken into account in the UCL competition every season.
I am sure, whoever the manager of Real Madrid is, the manager will succeed in making Real Madrid get the trophy. Because after all, basically Real Madrid itself has financial strength and thus, the manager can easily ask to buy the best players that can be brought in in the Real Madrid squad. After all, Ancelotti's success as a manager so far is also when Ancelotti manages to make the team get trophies, at least more teams are elite teams with good finances.
But anyway, when Ancelotti became the manager of a mediocre team with no financial strength, the results were also bad. So yes, in this case I personally sure whoever the Real Madrid coach is, the coach will still have a great chance of success. Because with the team having a squad with great players for the main players and second-tier players, it will make the coach still manage to get good results despite rotating players.