This is the main problem. Dortmund lost points against a relatively weak opponent. Even if Dortmund had lost points against Freiburg or Leverkusen, I would have said that Dortmund had some chance of winning the title. Now that their performance has been erratic, it will take a long time for them to get back on the winning track. In the future they will play against Frankfurt and Freiburg. They will also fail to score full points from these two matches.
It is chronic problem of Dortmund in past several seasons. They did not manage to maintain their good performance in a whole season while Bayern can do it. So Dortmund always end seasons with less total points than Bayern. They did not win title because of an unstable general performance and in this season, this chronic problem occurs again.
I don't expect Dortmund will fix it with players they have and with very stable and dominating performance from Bayern, Bundesliga trophy will likely be taken by Bayern, one more season.
Freiburg or Leverkusen won't be able to do better than Dortmund in my opinion.
Obviously Bayern will win this season, it was decided beforehand, no one can catch up, but I agree with you about Borussia. But think about it, any other team will be as unstable as Borussia, that's normal, and Bayern is a phenomenon of the modern world, that almost every time they win any team, but of course there are bloopers, nothing can be done about it.