Kompany must perform well next season to challenge xabi Alonso for the Bundesliga title. Leverkusen may maintain their performance from last season and rely on Xavi Alonso to lead them to victory. I feel that when it comes to the Bundesliga, Bayern Munich has the experience every season, but they did not receive hope and defeated Leverkusen last season, which will not happen again next season. I am confident that even if Munich does not win the championship, Dortmund will be the favorite to win it.
Kompany will try his best to improve Bayern performance and compete for the title. But you can't claim that Kompany or Bayern must perform well! The season isn't started yet, we don't know how Kompany will begin the new season. If Bayern can perform well in pre-season matches, it totally can't determine the performance in the league.
Sure, Xabi Alonso will be possible to maintain the performance of Leverkusen, whether he will repeat 'unbeaten' record or not. With the current squad of Leverkusen, I think Xabi Alonso still has a good chance to win again the domestic titles in this season. Anyway, it won't be easy because there must be tight competition from other teams. You're right, Dortmund also has the chance to win the titles. Dortmund looks good to build their squad, they bought some good players.
Regarding the chance to win UCL title, I am not sure if the teams in Bundesliga can win it. Bayern Munich and Dortmund just hired new coaches, new coaches sometimes get difficulty to manage the team in the first season. Meanwhile Leverkusen, they look like having no mentality to win UCL yet, I still remember how Atalanta could destroy their dream in the last UEL final.
Xavi Alonso's games are excellent, but they will most likely be defeated the following season, the other clubs will not allow this to occur. Bayern Munich are not as good in the UCL as they are in the Bundesliga, but if they enter the league and defeat Madrid, they will be serious contenders to win the UCL because Madrid is normally the favorite every season, along with Manchester City, but Madrid are more likely to win. Bayern Munich will try, but it will be difficult to win the Champions League trophy because there are experienced clubs in the competition who will easily beat them.
Real Madrid and Man City are always the candidates to win UCL. Real Madrid looks like having stronger squad, they have Mbappe now. Meanwhile Man City may try to win UCL and give the trophy for the farewell with Guardiola. Let's see which team to reach the final and win the trophy of UCL this season. I personally expect Real Madrid to win again UCL trophy, it will be the first UCL trophy for Mbappe.