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. Tuchel won UCL trophy and many domestic trophies.
However, I agree that we can underestimate Kompany. He was a great player at lest, he knows well football. I don't want to feel pessimistic, too. But honestly, I am not so sure that Kompany will bring big impact to the performance of Bayern Munich.
We must realize that the candidate of the winner of Bundesliga isn't only Bayern Munich and Leverkusen. Dortmund is also strong team, they always becomes a strong competitor for Bayern Munich. Moreover, Dortmund successfully sign a new machine goal currently, Serhou Guirassy. I assume Dortmund will be stronger in the next season.