Ancelotti wasn’t lucky with the players Eder Militao missed a lot due to injury, Mbappe had to adapt, and Bellingham and Vinicius weren’t in the kind of form we know them for. I think Xabi already has well developed tactics and excellent training sessions that will generally prepare the players for the start.
Real Madrid headcoach, Carlo Ancelotti was lucky enough to have the best players around and these players was determined to win games and lift trophies, they got it in them to come out in every game with stellar performance. What change in the Real Madrid team? We've not any scenario where the best team will not come out winning consistently at the top. Eder Militao was eager to play but base on his unfit momentum, we watch him crumbled several time and became one lesser on the pitch. He couldn't meet up the desirable expectations and this got him some flopping performance and stats. He's not only the one but others included.
Real Madrid is definitely not the same team as it was a few years ago. Remember, Real won three consecutive Champions League titles when Zidane was the head coach. I believe Xabi can motivate them and elevate the team to a higher level. They just need to stay healthy and be in top form.
In the history of Real Madrid, most of the managers who have served Real Madrid have been successful in their duties. Real Madrid considers many factors when hiring managers and they hire the best managers for their club. When a skilled manager takes charge of a very strong team, naturally the team and the manager will perform well together and the team will win big titles under the manager.
However, so far, no other manager except Zinedine Zidane has been able to win the UCL trophy three times in a row. Zinedine Zidane is different in this regard for Real Madrid. However, the one who is currently appointed by Real Madrid has enough skills to manage a big team and is also a former Real Madrid player, so I think he will win multiple Champions League titles again under him and Real Madrid.