But the problem is Heidenheim is still the same as other weak teams and only made a good start this season. In fact, they will still fall against a strong team like Dortmund and that is a definite guarantee. Just look at the opponents that Heidenheim previously defeated were only teams of the same level as them, namely Augsburg and St Pauli, so the 6 points they got is not something amazing.
There is no hope for Heidenheim to win and even if they take the lead first, Dortmund only needs to make a comeback to collect full points at home. Without Guirassy I think Dortmund can still put pressure on their opponents well and don't forget Dortmund still has Maximilian Beier who played well last season with Hoffenheim and of course he will not just sit back.
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.
Previously we also thought the same thing when Leverkusen were able to achieve consecutive wins and were undefeated in the league, but in fact we can see how Leverkusen, who was previously a weak team in the Bundesliga can able to show consistency in their performance in last season, what Heidenheim has achieved at this time of course not guaranteed to do like Leverkusen did last season, but looking at Heidenheim journey so far I actually hope they can give us a surprise this season, the match against Dortmund will clearly be the first test and also a challenge for them to maintain their position in top bundesliga standing, the current leagues in Europe has changed drastically where many teams that are considered weak are actually able to put pressure on the strong teams in the league, so it is not surprising that bookies no longer dare to give big odds to strong teams during this time.