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.
If a team loses every time and looks weak, they should work hard and fight. Yes, they can improve themselves, but unless one works hard, people will equate them with weakness and poor performance. Although he doesn't work hard, if he plays well with his team, he will surely win the match. Indeed, why not have a weak team, the condition is that they play with good performance and speed. If you play with such performance, you will definitely lose. If they win the match, no team gives the match easily to anyone. It requires hard work and good performance and if they succeed in that, you will be really happy. Yes, if the team that works harder then they deserve to win otherwise their efforts will be wasted.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.