The truth is I don't know how the MU allowed itself to be fooled by ETH at that time, however as I said before, for me he was the destroyer of the MU, and he caused so much damage that the team still hasn't been able to lift its head up, it's difficult to lift a team when it's like this, however for me Amorim has done what he could, what I didn't like was his treatment of Garnacho, it's not the way he did it, but those are very internal problems.
I believe no one is capable of knowing the future that is why Manchester United were unable to see that Erik Ten Hag would only make things worse. However Ten Hag did what he could which obviously wasn’t good enough and put the team in further trouble. Amorim is here now and has the opportunity to change things, hopefully he would be able to do so.
I wouldn't blame Ten Hag for all the mess he did, but the management because they saw his laxity that he cannot improve the team, but they went ahead to support him with getting overhyped players expensively just because he won City in the FA Cup finals. They should have known, Ten Hag isn't capable anymore. It was when everything was falling apart in the club that they didn't put any confidence in him. If not, they thought he is going to be the new coach to transform the team.