I heard this kind of speculation last season too, when they sold Haaland. Many said that they would not be as strong as the previous season because they sold one of their most important players. And they showed that it was wrong and they remained one of the clubs that had the second biggest chance after Bayern Munich, and even last season they almost won the title if only in the last match they could get full points at that time.
Undoubtedly its important players for Borussia Dortmund Bellingham and Haaland departures have had an effect on the team performance. Dortmund recruiting of young talent is their strength, but they might run into difficulties this year. I think They still have time to demonstrate their dominance in the Bundesliga despite a poor start. Their rivalry with Bayern Munich though might not be as intense. Dortmund chances of qualifying for the UCL are in jeopardy due to the improvement of other Bundesliga teams.
If only they had reduced the number of sales of their quality players and kept more within the club to achieve, I'm sure they would have achieved something impressive by now and maybe they could have won the Champions League for the second time. But that's them, business is business, if there is a player who has the potential to bring in a lot of money they will not hesitate to let him go, even if that player is a very scary specter and has contributed a lot to them while in the squad.
And yes that's Drotmund with all its business. Lol