Looking at Xabi Alonso's managerial career, one would not say he's doing badly especially when he was at Leverkusen, he was able to reform the team and bring them out of shambles to the successes they recorded using his 3-4-3 formation which was unique and popular for its counterattack abilities. He understands how to take advantage of a dysfunctional defense and midfield especially that which not firm and tactical, he will always find a way to send his players to attack the loopholes. He's never managed a big team like Real Madrid before, so I know his first el-classico will take much of his time and efforts in planning because despite being the head coach, he has the dignity of his team to protect. He's gathered enough experience when managing for the Leverkusen so I expect him to use much of such experiences on his games, going further. This season is really going to be interesting to see Madrid drag the season's title with Barcelona but even a seasoned coach like Ancelotti couldn't do better last season so it is more of an honorable challenge for Xabi Alonso to show his skills and steer the ship to their dream land.
One could argue he was hired by Real Madrid way too quickly though. I mean it is true that he did awesome at Leverkusen, there is no denying that and winning Bundesliga over Bayern Munich and going unbeaten all season, and having a 52 unbeaten streak with a team like Leverkusen shows that he had one of the greatest seasons a manager ever had, it's true that he was amazing.
But that was literally just one season, and that's it, he didn't do this for ten years before coming to Real Madrid, he had 2 good seasons, one great, one not so great but still pretty good, that's it, that's all there is to it. I am pretty sure it's going to be not that weird to see him struggle at Real Madrid because he is a young manager who had some experience, but not a lot.