Some talented players sold by Borussia Dortmund, I imagine if they prefer to keep them, then I think they will achieve great success.
Even if they are currently experiencing a very deep decline, I am not surprised by this, because previously I also predicted that something like this could happen at any time. Keep in mind that even though they are very good at finding potential young players, sometimes they are not lucky enough. They can't regret it, what they have to do is change what they have been doing.
That's how Dortmund makes a profit from the process of selling their players and it happened almost every season before. I don't think they can achieve club success in a short time even though most of the young players they don't sell, but if Dortmund keeps these young players in the long term this club should be much better than Bayern Munich because there are many potential players they have but they are not used to achieve club success and instead they only think about the benefits of the player sales process. This season we can see how Dortmund started to lose the competition in the top three positions in the standings and it is much more difficult for them to compete again.
What you are thinking is exactly what I am thinking, if Dortmund could keep every star player, of course they would have a squad full of stars and maybe even surpass the quality of players that madrid and munchen have had so far, but would they survive in the league if they kept their star players?
of course not my friend, Dortmund have never been financially strong and their ability to identify, develop and sell star players has been the only way they have been able to stabilise their finances so far, in fact I remember that Dortmund were so heavily in debt that even Munchen had to provide assistance to their rival team to pay off their debt, indeed, what was done by dortmund seemed to be a team that was concerned with profit, but actually it was no different from what was done by arsenal in the wenger era, which must to sell many of its star players in order to pay off the huge debt due to the construction of the emirates stadium, so I think each team has its own way to be able to maintain their financial stability all this time.