Dortmund doesn't really get lucky when they buy good and talented young players and sell them for a lot more than they bought them. It is a system as you noted and that is something Dortmund mastered over the years and is now the club I guess with the best transfer history maybe? I
I'm not really sure whether it's because they're not so lucky in this regard, or is it their ability to manage the team, manage and train the squad, and optimize it that's still not optimal? Because sometimes they have a very brilliant opportunity, but it's just wasted. several talented players were actually brought in by Dortmund, but it looks like they need a more suitable and appropriate tactic.