He should be able to achieve this again, now that he's coaching a big club with a much better quality of players than he had at Leverkusen. The typical difficulty for a coach is not having quality players, making it very difficult for them to achieve success. But Xabi Alonso is at a team that has everything, and it should be much easier to achieve success, although the challenges are also much greater. I also believe Xabi Alonso will be successful at Real Madrid, but not in his first season because competing in the Champions League is different from competing in the domestic league.
Being at a big club with so many star players certainly won't be easy for Xabi to lead Real Madrid to trophy success. There will certainly be many obstacles, such as managing players who are sometimes selfish, and other issues. This is compounded by the pressure from Real Madrid fans, who undoubtedly want Real Madrid to win the title, as last season saw Real Madrid fail to win a trophy.
His time at Leverkusen will certainly be different from now, but Xabi certainly has a good plan and strategy, which is why he is capable of being the Real Madrid coach. For his first season in the Champions League, my prediction is the same as yours. I also see Xabi Alonso needing time to adapt well at Real Madrid, especially in the Champions League next season. It will certainly be difficult for Real Madrid to win the title. But if Xabi can develop a good strategy, there is certainly potential for Real Madrid to win the UCL trophy. The players and coaches are certainly tense now and will be trying to develop their best strategies.