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.
Yes, it's true that Bayern Munich goalkeeper is a little weak, but it's not just support from the attackers, but the back line of defense is also able to help strengthen Bayern Munich's goal and several times Bayern Munich's defense players have saved the goal from opponent attacks and it pretty sure that in the next transfer season it looks like Munich will considering getting a new player on defense (goalkeeper)
Dortmund I think that this club will experience a decline in the early stages of the season and increase in the middle of the season and will drop drastically towards the end of the season and this happens every season or is consistent and unstable.
But lets just see what will happen to these two big club because I believe there are always surprises in every season, it could even be that surprises give Dortmund the luck to top the points table.