I don't really know why many people think that Bayern Munich's performances will decline or will not improve under Kompany as head coach next season. Kompany is not that experienced as a coach, but that shouldn't mean we judge him negatively. It would be better to allow the season to start and see their performances before rating Kompany as a poor coach. As for me, I believe that Bayern Munich will surely be in the race for winning the Bundesliga trophy next season. Bayern Munich will be a great challenge for Leverkusen, not to mention Dortmund. In fact, from my observation, I can't say if Dortmund will even be a good contender for next season's Bundesliga trophy, but let's see what happens.
I think it is normal if people are pessimistic with the performance of Bayern Munich. People expect that Bayern will hire a top coach who has a great experience with big teams and achieved many trophies. Conte and Zidane were 2 top coaches that people predicted to be the candidate of Bayern Munich coach for the new season. Surprisingly, Bayern board decided to choose Kompany who has no experience to manage a big team and never won prestigious trophies. The previous coach (Tuchel) is even still better than Kompany if we considered the career history and the achievements.