Bayern Munich wasn't at much lacking in their defence, but some additions and selection will help strengthen the team, a club with a slim defense line is likely to face great despair from their oppositor. With Kompany as the coach and with iconic position as him being ones a player, I think he would be a lot more defensive and this will help him not to conceive early goals and wide margins.
My opinion is the opposite, I believe that with Kompany Bayern will become a more attacking team, perhaps as it was under Negelsmann, and the reason is that Guardiola’s school will play a role here. But I agree that Bayern could have done better with their defence, it has often let them down in crucial moments, and they shouldn’t rely only on Neuer, he also makes mistakes.
Kompany is 38 years old. He hasn't achieved anything yet, but he got an invitation to Bayern. So why did Germany's top club choose such an inexperienced coach? Some football experts explain it like this.
Perhaps the answer lies in the trend towards attacking football. We see that in Europe it is rather dominant teams that succeed. Kompany was putting on a controlling football similar to the City/Brighton/Bayer style. This style allowed them to win the Championship with young players. But Kompany lacked the high calibre of players to be successful in the EPL. And now he will have absolutely top level players.