I was actually disappointed at Bayern Munic for loosing to Mainz but as it is football, such things happens to male the sports interesting and full of surprises. On the other hand, I love the energy with which they bounced back by humiliating RB Leipzig with 5:0. This results shows that Bayern Munic losing to Mainz might actually be a mistake, although, it is a costly mistake. Bayern Munic have good opportunity to win the German Bundesliga this season even though they still have many teams to contend with.
Bayern Munich might not be the delivering results like many of us would have wanted but the truth is that they've been the best German team this season. After the 2:1 defeat at Mainz which you said you were very disappointed at, Bayern Munich convincingly thrashed RB Leipzig 5:1 six days later in the league standings.
Vincent Kompany is still trying to figure out which of his tactical approaches brings out the best from his players so you should expect him to lose some matches while experimenting.
Bayern Munich I believe will win the league this season and that would be a great achievement for Kompany if he achieves that.