For me it is rather the cult of personality that always gets you in these situations. Probably it is because of the unparalleled impact Ferguson had on your club but you're always looking for that one strong leader who saves you or the one player who lifts you on the next level. In this case, you have granted Ten Hag more say on transfer activities than any other manager in the world including Guardiola and Klopp. I mean, after ages you've finally adapted the best practice of implementing a DoF and shortly after you make him a lame duck again and grant the last authority over transfer activites to the head coach.
Ten Hag's seeming favoritism of Antony is arguably what started this whole story but solely looking at the conflict itself, did Sancho's misconduct really justify banning him indefinitely and demanding a walk of shame? A suspension of one or two months seem short in hindsight but at the time, it would have been seen as very strict. I mean, I struggle to recall any player who was banned by his own club for more than one game. But Ten Hag not only took it a level further, he chose to make it personal on top of it. I don't know why you allow him to roam that freely. It is an ego trip that cost the club millions already. If Dortmund didn't know that there was no way back for Sancho at United, your bargaining position would have been much, much better.
I don't think there's any other club in the world who is so focused on individuals as you. Always a player on the market that is far too good to miss out on. Immovable support of the manager. And when things go south, it turns towards the other extreme ("make an example out of Sancho and let him rot on the bench for the next two years, feck the 40+m that will cost us").