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
Bayern Munich remained the giant of bundesliga because they focus on the title more than any other club. Borrusia Dortmund are known for the potential important players they have in the club; the shocking part is that the club continues to sell these valuable players to elite clubs; there are significant players that have been sold out by these clubs, players like Robert Lewandowski, Jadon Sancho, Erling Haaland, and now Jude Bellingham has joined the race. The club isn't concerned with winning the Bundesliga; all they want is to continue making huge profits from the transfer market, and with their predicted budgets, they're doing just well.