The Bundesliga title still looks quite easy for Bayern Munich to defend, even though currently Bayer Leverkusen and Sttugart are still quite consistently in first and second place. It's only been six matches and we often see that several clubs have difficulty maintaining their best playing performance, apart from the reasons why several players have suffered injuries and there are other factors that might make it difficult for them to appear consistently. Bayern Munich is still on track to win the Bundesliga title and I believe they are still one of the strong candidates this season.
Everything will depend on how consistently Bayer and Dortmund can play throughout the season. Bayern have problems with defense (in particular with the goalkeeper), but they can offset this with good attacking play, and they also have a strong bench. Dortmund traditionally experiences slumps after the middle of the season, in most cases due to player injuries, and we will soon see what Bayer is capable of.