the file to edit is simsettings.ini. it needs some (probably a lot of) experimenting to get balanced results, but it's doable. if you raise domestic prestige and competition influence, the likelihood of bigger teams getting better results do increase.
i just realized that the tweaks of the thread i posted above work in newer fifas aswell, at least until 16 (not sure about 17). all of them use the same parameters to simulate their seasons.
my values are possibly not something you would like though. ime, results tend to get a bit more random. i only find strange that you had dortmund in 8th with vanilla simsettings. it might have been just a very odd season. even with my settings, they're practically always top 4 at the end of the season.
hmmm. it seems like dortmund has really a tendency to underperform, even with my sim tweaks. i might have been mistaken when i said "they're practically always top 4".
i simulated four bundesligas to check, with my settings. bayern won the league twice, wolfsburg once and schalke once. bayern finishes were 1st, 3rd, 1st, 2nd. but dortmund finishes were 7th, 2nd, 6th, 4th. a bit below par for them.
what you can do is editing the database with db master or cm. scroll to the "teams" tab and increase dortmund's domestic prestige (maximum is 20). this will force them to perform better in the simulations.
anyway, if you're having no competition in the table, you might consider increasing your difficulty level too. with the database tweak, the most you will get is bringing dortmund to the level of the teams that were chasing you before. but if the others were no competition before, dortmund won't be as well.
oh. and if you edit the database, you have to start a new career =(
btw, i'm not sure if any of those edits is possible in fifa 17. i'm only familiar with the db and file structure of the games released until fifa 16, because the structure was the same, but it seems like some things changed for this new engine.