Bundesliga can be categorized as a competitive league. The weak teams you mentioned do not mean that they cannot provide a surprise, including Heidenheim, they could show it later at Signal Iduna Park, and I do not agree with the definite guarantee that you said. If it is true that Dortmund will definitely win, does that mean Heidenheim cannot win? How do bookies provide odds if victory is certain in Dortmund's hands, and I as a bettor would be happy if it was guaranteed. 
In my opinion, both teams have a chance as long as they can maximize the existing opportunities by focusing and working hard in the match.
Every club wants to win, there comes the challenging opposition. Borrusia Dortmund, Bayern Munich and Bayer Leverkusen are the only promising clubs that are capable of lifting the Bundlesliga title this season. They’re competitive enough and any club sitting at the top is mostly temporary and will definitely come down when the time is triggered. Bundlesliga is not some random league that average clubs record thrilling winning against the elite ones, it takes only hard work and consistency for these average clubs to boosts their form towards their oppositions.In my opinion, both teams have a chance as long as they can maximize the existing opportunities by focusing and working hard in the match.