I understand what you are talking about. For me, there is nothing wrong with Xabi Alonso coaching Bayern Munich next season because Bayern Munich and Bayern Leverkusen are not on the same level. Xabi Alonso's good performance at Bayern Leverkusen is for him to get a bigger contract from big clubs, which is already working out for him.
However, if Xabi thinks the same thing as me, then he can stay at Leverkusen, because Leverkusen itself is certain to get a place in the Champions League next season. That way he can show that he is a coach who can really compete, he has to prove that because so far many people have said that this is Xabi's luck.
Xabi Alonso has proven himself with Bayern Leverkusen this season in the Bundesliga. With the help of Xavi Alonso, Bayern Leverkusen is one of the most consistent clubs in the top five leagues. Bayern Leverkusen is still unbeaten in the Bundesliga, and they are leading Bayern Munich by 10 points in the Bundesliga table. I don't see this as luck, but as someone who knows what he is doing.
The problem is, when coaches and players have given great success to the team, but it happens to Bayer Leverkusen which is basically not a rich team. So, it will make it difficult for Bayer Leverkusen to give big salary increases to coaches and players who have managed to deliver impressive results throughout this season. With this factor too, it is not surprising that so far when great players and coaches have succeeded in mediocre teams, then these great coaches and players will leave when the transfer market opens. Therefore, if for example Xabi Alonso really leaves I think it is a natural choice but unless, if Xabi Alonso is really willing or loyal to Bayer Leverkusen, then Xabi Alonso could choose to stay at Bayer Leverkusen. But anyway, Bayer Leverkusen themselves have stated that Xabi Alonso is available to leave, because Bayer Leverkusen themselves have no efforts to keep Xabi Alonso.