Xabi Alonso made an excellent decision to continue with the team next season. Leverkusen will play in the next Champions League, they will need a coach like Xabi Alonso because he has played in major competitions such as the Champions League. I can't wait to see the club compete with the clubs from other leagues, as we have seen how they competed with Bayern Munich for the Bundesliga title race this season. You're right, they need to add more players next season, so they shouldn't be eliminated so easily, because they will face difficult challenges in the next Champions League if they meet a major team like Real Madrid or Manchester City, we don't know if their current players will have strength to play this way next season.
This is an unexpected decision, he had so many opportunities to move to another more top club, but he decided to stay at Bayer. I don’t know what to say, in my opinion this is not the best decision he could make, perhaps he is counting on the fact that next season he will be able to repeat all the success again. I think that he will not be able to repeat the same thing next season, perhaps this is a mistake, especially if the next season can be worse, he will not have as many offers as now. But this is his choice, apparently he just doesn’t want to change anything.
I think the best decision or not is just a matter of comfort and Xabi targets for next season, he seems to want to take Leverkusen further in the UCL with his own hands. Several offers have now been closed, including Liverpool who have stopped fighting for Xabi. Bayern Munich will definitely do the same thing where they will shift their focus to finding a replacement for Tuchel. Imo if Bayern Munich top officials are not shy, maybe Nagelsmann is the right person to manage this team like before and Nagelsmann understands exactly what the team needs. But due to problems in the past I'm not sure it will be fixed. Bayern Munich's coaches have big demands, they don't want this club to be in bad condition and they also don't want this club to go through a transition process. So the choice in the future must be more than what Tuchel can provide now.