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.
You have a good point and we all know how far such an approach has taken them and they are still always the voice to reckon with in the league. Borussia Dortmund has been good at that, they make money and still perform well, and I've not seen a club in Europe that made it as obvious as them and still replicate consistent success to the top runner-up even if they did not win the trophy. They've not yet delivered spectacularly this season but will still do as the hope is high, and no club has won them as well.
But they should have performed better against Bochum and Heidenheim instead of drawing such clubs. Playing with stronger clubs might be an issue if they continue like this.