Hi King7Eric, thanks for putting the time in to formulate your thoughts in more detail. I hope you are fine with me disagreeing on a few aspects.
Here's the thing mate and I had tried framing it to some other Dortmund fan on here as well who got set off with it. I think we can all agree on the following-
1. With or without Sancho, BVB are not likely to win the league. They will finish in a CL qualification spot and in the CL they'll reach the RO16 or QF. Of course, anything can happen in football but these would be there realistic ambitions for this coming season. Keeping Sancho or letting him go does not change those ambitions. Keeping or letting go Pogba does affect Utd's ambitions. With him we can probably aim higher than we would without him. Utd are not happy with our current standing in the game, whereas BVB seem perfectly happy where they are as evidenced by their constantly selling their biggest players. If you really have ambitions of winning trophies regularly, you don't let go of your best players irrespective of the price.
I think your first paragraph might be the worst right at the start in my eyes. Maybe as a fan of one of the richest clubs in the world it is not a reality you are aware of but barring maybe 10 clubs in the world every single club in professional football has to sell their best players eventually because they aspire to play for and with the best. I would hope we can all agree on this. Dortmund are one of the clubs that have to deal with this reality and yes, they have to sell players because they want to move on to richer or more successful clubs eventually. That does however not mean that the club has no ambitions. This might actually be the point people take offense with here the most, me included. It's like telling United fans to shut up because they might be happy to have qualified for the CL this year and tell them that they did not even win the title so why even bother. Every club has some kind of ambition and for that they of course need the best players available. For Dortmund this means a balancing act of keeping players to remain competitive and sell them if it is the fiscally responsible thing to do.
The second thing you say here is that Sancho staying or leaving does not change the ambitions. That is very much not true, he is a fantastic player and of course he elevates the level of Dortmund's attack. They might not win the title next season either, it is far more likely Bayern will have it again. But I am sure they nevertheless want to try take the fight to them again and for that the chances are very much improved if Sancho stays. So no, Dortmund are not "perfectly happy where they are", but they are also not delusional. They aspire to improve and keeping Sancho would in the short run help than more than selling him. As a short aside I am pretty sure that they would only agree to selling him for a specific fee because that is what they agreed on with the Sancho camp.
2. In the last 20 years, Ronaldo and DDG are the only 2 players whom Man Utd wanted to keep, but yet agreed to sell. SAF wanted to sell the likes of Beckham and RVN and well wanted to get rid of ADM. BVB on the other hand constantly sell their top players, whatever be the reason. The likes of Sahin, Hummels, Gotze, Kagawa, Mkhi, Aubameyang, Dembele, all these are of the top of my head. They constantly act as a feeder club for the top clubs of Europe, so why get offended when someone calls them that?
This basically only reflects the situation considering the vastly different financial prerequisites these two clubs have. Also these transfers basically all need to be evaluated on a case by case basis as the financial situation in Dortmund changed quite drastically in the timespan that they too place in. So yes, Dortmund have had and will for the foreseeable future need to sell players when they want to leave the club and it is financially compensated. That still does not mean that it is fun to be called a feeder club by opposition fans as it is quite obviously used as a derogatory term. The implication is that there is no ambition which in my opinion is not true as I explained before.
3. Even if they keep Sancho for a year, he is not going to spend his entire career at BVB. He may leave next year but he will go for sure. Now given that its likely his value will go down given he will have a year less on his contract and his staying for a year is unlikely to lead to BVB winning the league or CL (of course they could surprise us but we'll all agree it will be a major shock), it leads people to question what is the point of keeping him here? Why not reduce your demands a little bit? So that you get your money and buy a replacement and carry on with your model of grooming and selling players while staying the 2nd best team in Germany.
This is basically the same argument, so I will make it short, keeping Sancho helps Dortmund pursue their sporting goals in the short term and increases their chances for a miracle result. That is what sports teams should strive for in my opinion.
It is these 3 points that make Utd fans feel that BVB are just drawing out this saga unnecessarily in a move that benefits no one. If its Villa acting like this with Grealish, then I could understand because Grealish staying or leaving is likely to be the difference between Villa staying up or getting relegated so you can understand why they would stick to their demands. Sancho staying or leaving isn't likely to change BVB's standing so it all seems like unnecessary posturing.
So I think I made clear that we are not in agreement on this, I hope you can see my side or the side of the club a little better. I do not thing Dortmund are posturing to drag the saga, they are posturing to keep their player.