There's no proof yet, as preseason results can't be used as a benchmark for measuring a team's strength.
Xabi Alonso still has a lot of potential, and many people have differing opinions on that. Some are skeptical and others are optimistic. But personally, I think we should wait until the competition gets underway and see the results of the Real Madrid team he's built.
Overall, Xabi Alonso is a quality coach, but coaching Real Madrid is a bit different because the pressure can negatively impact Xabi Alonso's mentality, especially as he's a young coach.
Real Madrid has all the resources that a good coach like him need to become successful. I don't see any pressure that will be on him to the point the he will make decisions that will affect the team performance negatively. Alonso was able to work something out of nothing with Leverkusen. This gives me more confidence in him that he will take the team to a greater height.
To me, anyone thinking that Xabi Alonso will not be able to do anything in Real Madrid doesn’t really know what Xabi Alonso is capable of. If we all could remember what he did in Bayer Leverkusen, no one would say the pressure will be too much for him, because Xabi Alonso is a talented and smart coach. He has more than he needs in Real Madrid, so I don’t think it will be hard for him to make Real Madrid the strongest team to face this season. For those doubting, let’s wait and see how the season will be. If not, even from the pre-season, you will know that Xabi Alonso is unstoppable.