There is a massive difference in managing a top team and any team from expected position 5 and below.
Take Benitez, he is a quality coach. With Everton he is expected to finish from 5th to 10th. That means that he can afford to have some silly dropped points during the season, some bad performances, can have some players that aren't quite up to the standard of Everton, some coaches that, similar to the players, might not be up to Everton's standard yet. All that means that from the manager through the coaching staff to each player, they don't need to have that absolutely top top athlete mentality of a true winner.
Now compare Everton to United.
We are expected to win every game, or at the very least to trouble every team. To win silverware. To drop only a few points in the season and to do so playing quality football. That means that our manager has to be the same caliber as Klopp or Guardiola or Tuchel. Our coaching staff needs to be best in class for every area of training. And our players need to be the very very top.
Ole has no pedigree as one of the best managers in the world. He has never managed at a high standard and has won nothing, even though he has some of the best players in the world.
He does not know how to be ruthless in removing players and coaching staff that are clearly not good enough to be at the best team in the world.
He does not know how to affect change in a game with the use of substitutes.
And he does not have the ability to reach the required standard any of these either.
We have all worked in a company where the work gets done well despite the manager being crap, but when you get a whole business that is run by idiots it goes bust.
Mark my words... if the Glazers, Ole and his coaching staff do not leave our club very soon, the future belongs to Liverpool, Chelsea, City and Newcastle.