Bayern Munich's defeat proved that Kompanty is very dependent on striker Harry Kane. When Kane was absent, Bayern Munich had difficulty breaking down the opponent's defense, in this case Mainz's defense, to score goals. This can also be seen from the actual game statistics. Bayern Munich dominated the match with 69% ball possession and released 13 shots, but they only managed to make 1 shot on target and it was ineffective. Without Harry Kane, Bayern Munich could not win the match and this was their first defeat after 13 matches without defeat.
On the other hand, in this match Mainz also appeared very effective and clinical. It was seen that they tried 8 attempts at kicks and 4 of them were on target, even though they only got 31% ball possession but they played very effectively. In the end, Mainz gave Bayern Munich their first defeat in the Bundesliga, this defeat not only made Kompanty have to learn from his mistakes but he also had to be able to play the role of all players without having to rely on just one player. So if there is an injured player he can utilize the potential of other players.
Honestly Kompany depends entirely on the talent of the players to begin with. Bayern Munich is already a great team with a lot of talent and the only reason why they are doing any decent is because those players are so talented, without Kompany and with anyone, you or me doesn't matter, they would have done this good too, Kompany has absolutely nothing that he can show as his contribution to this team.
Not like Bayern would have done any differently with any other manager, they are always good and they always get this much points anyway. So, this isn't a shocker and I believe he was a mistake and they shouldn't have hired them and we can't really consider this to be a great addition, Kompany should be fired if you ask me.