Xabi Alonso has proven that he can build a team with even strengths across all departments when he was coach of Leverkusen, so I think he could do the same thing again with Real Madrid in the future.
At this point, we can't make any judgments because Xabi Alonso is new to Real Madrid and still needs time to adapt.
Regardless of who Xabi Alonso chooses, I'm quite optimistic that Xabi Alonso can make Real Madrid even better.
And it's also important to remember that Real Madrid are the Champions League champions, so they must remain a force to be reckoned with no matter the circumstances.
The difference was that at Leverkusen he had a "team", here he has bunch of stars, not a team. So his work right now is not strategy, not bench, not substitution, not formation, nothing like that on the field at all, this team could win anyways. The thing he has to do right now, is to make sure that he can battle the ego of his stars, and make sure that they can cooperate together well enough and even the stars do end up running.
Like they can't just let Mbappe and vini stay upfront and not go help with defense. If there is a press, then there is a press, they have to press and they have to get the ball back, they can't have Mbappe and Vini just watching defense. Or for example if there are passing, and no "max two times touching the ball" etc, so they are passing a lot, then yeah, Mbappe can't just get the ball run and shoot, he has to pass and learn to be a team player.
At Real Madrid, it's not enough to play good soccer. It's also about satisfying egos, handling the press and winning trophies. This pressure is much greater than what Alonso experienced at Leverkusen. Alonso has a lot of potential to succeed in star management because he knows this environment as a footballer and he is intelligent. Xabi Alonso is also a former Real Madrid player. He knows the culture of the club and the dynamics in the dressing room. This could help him build a natural relationship of respect with the players.