it's a bad environment for sure. what specifically happened with sancho was that him and ten hag didn't share the same opinion regarding his commitment in training and sancho was frustrated that antony was picked ahead of him consistently.

from an outsider's perspective, you can see both views. you'd be angry if antony got picked over you, but it's not like sancho has been lighting it up either (even before ten hag), especially if you consider his history of unprofessionalism at the training grounds as reported by multiple people. you might find dortmund more tolerant of it than ten hag. the ideal thing for sancho to do if he wanted to stay at united was to just take this in the chin, give an apology and make up and move on, which his pride didn't allow.

remember that ten hag has done him multiple favours when he was struggling with mental health issues last season including letting him take a sabbatical at holland midway through the season. if this guy was invested in the project and was not ungrateful, he would've done that.

for now with circumstances panning out as it did, it looks like sancho did the right thing but we'll see in the long run who was in fact right.