In essence, in my opinion, Erik Tag Hag must be stricter with players who cannot show their best game by substituting these players, not just disciplining players who are disobedient.
Erik Ten Hag's attempts at instilling discipline is a bit over the top imo, i know that as a manager you have to be in control of the dressing room in order to get good results, but you have to understand that these players are also human beings and adults as well, you don't publicly throw your player under the bus (like he did with Sancho), and expect them not to react (like Sancho did).
Many people has jokingly started saying that Erik Ten Hang likes discipline than winning matches. Everyone knows that he is that strick, even from Ajas. There was no much big guys in Ajax. So you may decide to treat them like high school students. For a club like Manchester United, a coach should be more of a Father like Sir Alex Faguson than being strict like a soldier. No matter how strict you are, if you don't win matches, you are nothing. You are hired to win matches and trophies and not to be a disciplinarian.
Remember how he also treated Ronaldo, who is arguably the greatest footballer to ever play the game, if Ten Hag has been overly successful in his time at Old Trafford, then nobody would remember all of this, but he is not succeeding as people would expect, thus leaving him with egg on his face. Erik Ten Hag should concentrate more on getting his tactics right, than on disciplining players.
He nearly brought down the career of Ronaldo, if not that Ronaldo acted so quickly to liberate himself. What Erik Ten Hang did to Ronaldo was one of the causes of Ronaldo seeing bench in the world cup.