Bayern got three players from Dortmund this past decade, none of them after 2016:
Lewandowski - decided to go there on his own, huge success
Götze - career faded away after he went there; returned three years later
Hummels - was ok for Bayern, nothing more; returned three years later
The only "homerun-hit" was Lewandowski. The other two didn't really tip the needle in favor for Bayern at all.
Since 2016 all the other Dortmund "stars" that left went to Arsenal (Aubameyang), Chelsea (Pulisic), Barcelona (Dembele), City (Gündogan) and United (Mkhitaryan).
The problem isn't really Bayern raiding their league, since all their recent top transfers have come from abroad (Sané, Hernandez, Tolisso, Davies etc.).
The problem is that the international transfer market has been poisoned by all kind of sugar-daddys and investors taking over PL clubs (and PSG), making them so much more financially potent compared to you oldschool Bundesliga, Serie A or La Liga team.
Clubs like Real, Bayern, Barca and Juve can still compete financially, which then affects their respective league of course, since those big clubs can keep their stars, while all other clubs from their leagues lose players to the PL.