Dortmund strategy of using player resale to achieve financial success is debatable and some may think it takes away from the spirit of the game. But there is no denying that their approach has paid off enabling them to challenge Bayern Munich for first place. Dortmund inclusion among the contenders brings an intriguing dynamic to the football environment even though many supporters desire teams who put sporting success before financial success. It will be interesting to observe how other teams respond to the changing landscape of the game as they attempt to challenge Bayern hegemony and possibly shift Dortmund standing.
I think their approach is mainly good for the financial situation of the club but for the longterm development in terms of competitiveness and success of the team it is not really great in my opinion. Dortmund is buying young and promising players from the biggest clubs where those players don't have a chance to play regularly yet. In Dortmund they can play and if they are doing great their market value increases significantly like for example in the case of Erling Haaland or Jude Bellingham. Then Dortmund sells those players with a huge profit, which is great for their financials. It is not good for the quality of the squad though obviously and for example in the coming season Dortmund does not have a single world class player anymore because Hummels and Reus are getting old.
In the long term it is really bad if Borussia dortmund always does this because there are no reliable players or senior players who can bring Dortmund to win trophies and titles in the champions league or European league.
However, this has become the hallmark of Borussia Dortmund looking for academic players and educating them until they have strong new talents like Haaland after that they are sold and looking for young players again to be given directions to become reliable players and sold again.
Maybe this is Dortmund's strategy to get used to getting reliable players by scoring themselves instead of wasting a lot of money just for top players who don't guarantee a good contribution in the future.
I am sure that in the future Borussia dortmund will show its strength when it is serious about getting trophies in several big leagues without selling its best players