Xabi showed that he made the best contribution at Leverkusen which succeeded in bringing Leverkusen to victory. Their performance might be slightly improved because as we can see, in the Champions League, all teams have their own unique skills and strengths that are not easy to beat. What is clear is that I believe that when a coach like Xabi Alonso still gives full support to Leverkusen then there is still a chance to win.
Since the coach was at Leverkusen, Xabi Alonso was able to improve Leverkusen's performance significantly and last season Xabi Alonso was able to give Leverkusen 2 titles, even so, international competition is not an easy competition. We can see how difficult it is for Leverkusen to get through each round in the Europa League but they failed when in the final and next season Leverkusen will face more difficult competition playing in the Champions League which contains the best clubs from their respective leagues so it is not an easy task for Xabi Alonso to get this prestigious title amidst the competitive competition.
But I believe Xabi Alonso will do whatever is best for his club and it looks like Xabi is adding several players to fill several gaps which he thinks are still lacking. I believe Xabi has a magical ability to improve the performance of his players so as long as Leverkusen is coached by the same manager I don't think I'm worried about Leverkusen's performance next season, whether in the Bundesliga or in the Champions League. For me, just defending the Bundesliga title is enough to end the season well.