If we think about Vincent Kompany when with Burnley and Bayern Munich, actually it's something unfair. From the competition for each league is very different and in a condition of the squad is also different. Although Bayern Munich has a much more professional squad, but there is something we don't know that makes Bayern Munich a little difficult to get back to get the bundesliga title.
As you said in the weak defense that is the main problem at the moment. Vincent Kompany has tried to improve these weaknesses and if they still have the same performance, Vincent Kompany must be demanded to find the problem and immediately fix it. Pressure like this that usually makes the coach difficult to find the right strategy.
It is not easy for Vincent Kompany in time to be able to change everything I think everything takes time and a significant process of change but what must be admitted now is that we have seen a little different from Bayern's playing style since being coached by Vincent Kompany and I think if that continues then they will be able to make better changes.
And I still don't say that Bayern will have a hard time winning the Bundesliga title this season and even now I think they are more favored than Leverkusen.
Regarding Vincent Kompany's coaching which is different from the previous team of course has a significant difference because the squads of the two teams are different, so the tactics and playing style that are seen will also be different.