I don't agree with you because a palyer like Juge Bellingham is important for any team and Dortmund surely spent too much for growing a palyer like him because he also had a good performance when he was playing on that team and now you can see this palyer is even shining in Real Madrid. But Drtomund can still be on top of table Bundesliga table with or without Bellingham in their team.
Good players results in brilliant performance for the entire team. Edin Terzic knows what's valuable gone this summer all because the club more interested in generate significant good figures in the transfer window. However there's always a ground to settle for what's left with them by recruiting new backup players that would definitely be ready for the market in the forthcoming years. Jude Bellingham was a prominent player for Borrusia Dortmund, gaining enough experience and playing like a pro on the pitch for Die Borussen Die Schwarzgelben.
Not only Belllingham but Dortmund has given birth to quite a number of talented players and they always sell it when there are teams who dare to offer high prices. Although able to replace with other players, but I think the concept that De Borrusen built was quite brilliant because in addition to pursuing achievements but they also always won business, they were also always able to be the main competitors in the Bundesliga.
But besides that, players who managed to have a good performance in Dortmund, not all of them can also succeed at their new club. Perhaps a small example also happened to Jadon Sancho who left Dortmund, and then joined Manchester United. But what happened was like a failure and thus, there are still players who fail in their new teams. Although, we will always bring up players who succeeded in their new teams after leaving Dortmund like Lewandowski, Bellingham and many more. But the truth is, not everything goes well but indeed, basically Dortmund always has a way of continuing to produce great players in every transfer window.