And if Guraissy performs well at Dortmund next season and competes as top scorer, Dortmund will sell the player to another club to make a big profit

at least that's Dortmund's way of prioritizing its business of selling talented players at high prices even though he bought Guraissy at an affordable price from Stuttgart, so Dortmund will promote this player next season by highlighting his performance to attract the attention of other clubs.
Not at all surprised by Dortmund's habit and I think as a business club they know what to do. Instead of giving Guirassy a long time, when an offer comes in from a big club and even wants to redeem his clause, Dortmund will be very happy to let him go.
I think it is still quite difficult for any team to match the prowess of Dortmund management when it comes to player business and it looks like they will continue to do so forever. What makes me wonder, are the fans silent about the behavior of their beloved club? even though if Dortmund wants to keep their players then it will be much easier for them to win the title. But again, being in the top 4 in the Bundesliga seems to be enough to make them happy.